diff --git a/.travis.yml b/.travis.yml
index a315789c..bd8ad0b1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,7 +16,9 @@ install:
   - pip install -e .[test]
   - pip install codecov
 
-before_script: rethinkdb --daemon
+before_script:
+  - flake8 --max-line-length 119 bigchaindb/
+  - rethinkdb --daemon
 
 script: py.test -n auto -s -v --cov=bigchaindb
 
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 92137572..cf3a552c 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -82,7 +82,7 @@ How? Let's split the command down into its components:
  - `install` tells pip to use the *install* action
  - `-e` installs a project in [editable mode](https://pip.pypa.io/en/stable/reference/pip_install/#editable-installs)
  - `.` installs what's in the current directory
- - `[dev]` adds some [extra requirements](https://pythonhosted.org/setuptools/setuptools.html#declaring-extras-optional-features-with-their-own-dependencies) to the installation. (If you are curious, open `setup.py` and look for `dev` in the `extras_require` section.)
+ - `[dev]` adds some [extra requirements](https://setuptools.readthedocs.io/en/latest/setuptools.html#declaring-extras-optional-features-with-their-own-dependencies) to the installation. (If you are curious, open `setup.py` and look for `dev` in the `extras_require` section.)
 
 Aside: An alternative to `pip install -e .[dev]` is `python setup.py develop`.
 
diff --git a/bigchaindb/__init__.py b/bigchaindb/__init__.py
index 1276f9a5..dc31b148 100644
--- a/bigchaindb/__init__.py
+++ b/bigchaindb/__init__.py
@@ -11,8 +11,8 @@ config = {
         # Note: this section supports all the Gunicorn settings:
         #       - http://docs.gunicorn.org/en/stable/settings.html
         'bind': os.environ.get('BIGCHAINDB_SERVER_BIND') or 'localhost:9984',
-        'workers': None, # if none, the value will be cpu_count * 2 + 1
-        'threads': None, # if none, the value will be cpu_count * 2 + 1
+        'workers': None,  # if none, the value will be cpu_count * 2 + 1
+        'threads': None,  # if none, the value will be cpu_count * 2 + 1
     },
     'database': {
         'host': os.environ.get('BIGCHAINDB_DATABASE_HOST', 'localhost'),
diff --git a/bigchaindb/commands/bigchain.py b/bigchaindb/commands/bigchain.py
index 40891416..d52131ab 100644
--- a/bigchaindb/commands/bigchain.py
+++ b/bigchaindb/commands/bigchain.py
@@ -82,7 +82,6 @@ def run_configure(args, skip_if_exists=False):
             conf,
             bigchaindb.config_utils.env_config(bigchaindb.config))
 
-
     print('Generating keypair', file=sys.stderr)
     conf['keypair']['private'], conf['keypair']['public'] = \
         crypto.generate_key_pair()
@@ -162,7 +161,7 @@ def run_start(args):
 
     if args.allow_temp_keypair:
         if not (bigchaindb.config['keypair']['private'] or
-                                  bigchaindb.config['keypair']['public']):
+                bigchaindb.config['keypair']['public']):
 
             private_key, public_key = crypto.generate_key_pair()
             bigchaindb.config['keypair']['private'] = private_key
@@ -170,7 +169,6 @@ def run_start(args):
         else:
             logger.warning('Keypair found, no need to create one on the fly.')
 
-
     if args.start_rethinkdb:
         try:
             proc = utils.start_rethinkdb()
diff --git a/bigchaindb/commands/utils.py b/bigchaindb/commands/utils.py
index 6619da6d..573ba785 100644
--- a/bigchaindb/commands/utils.py
+++ b/bigchaindb/commands/utils.py
@@ -14,7 +14,6 @@ from bigchaindb import db
 from bigchaindb.version import __version__
 
 
-
 def start_rethinkdb():
     """Start RethinkDB as a child process and wait for it to be
     available.
diff --git a/bigchaindb/common/transaction.py b/bigchaindb/common/transaction.py
index 41d8a30c..c87b9864 100644
--- a/bigchaindb/common/transaction.py
+++ b/bigchaindb/common/transaction.py
@@ -3,13 +3,13 @@ from functools import reduce
 from uuid import uuid4
 
 from cryptoconditions import (Fulfillment as CCFulfillment,
-                              ThresholdSha256Fulfillment, Ed25519Fulfillment,
-                              PreimageSha256Fulfillment)
+                              ThresholdSha256Fulfillment, Ed25519Fulfillment)
 from cryptoconditions.exceptions import ParsingError
 
 from bigchaindb.common.crypto import SigningKey, hash_data
 from bigchaindb.common.exceptions import (KeypairMismatchException,
-                                          InvalidHash, InvalidSignature)
+                                          InvalidHash, InvalidSignature,
+                                          AmountError, AssetIdMismatch)
 from bigchaindb.common.util import serialize, gen_timestamp
 
 
@@ -38,17 +38,15 @@ class Fulfillment(object):
                     TransactionLink`, optional): A link representing the input
                     of a `TRANSFER` Transaction.
         """
-        self.fulfillment = fulfillment
-
         if tx_input is not None and not isinstance(tx_input, TransactionLink):
             raise TypeError('`tx_input` must be a TransactionLink instance')
-        else:
-            self.tx_input = tx_input
 
         if not isinstance(owners_before, list):
             raise TypeError('`owners_after` must be a list instance')
-        else:
-            self.owners_before = owners_before
+
+        self.fulfillment = fulfillment
+        self.tx_input = tx_input
+        self.owners_before = owners_before
 
     def __eq__(self, other):
         # TODO: If `other !== Fulfillment` return `False`
@@ -98,6 +96,14 @@ class Fulfillment(object):
             ffill['fid'] = fid
         return ffill
 
+    @classmethod
+    def generate(cls, owners_before):
+        # TODO: write docstring
+        # The amount here does not really matter. It is only use on the
+        # condition data model but here we only care about the fulfillment
+        condition = Condition.generate(owners_before, 1)
+        return cls(condition.fulfillment, condition.owners_after)
+
     @classmethod
     def from_dict(cls, ffill):
         """Transforms a Python dictionary to a Fulfillment object.
@@ -216,14 +222,13 @@ class Condition(object):
             Raises:
                 TypeError: if `owners_after` is not instance of `list`.
         """
+        if not isinstance(owners_after, list) and owners_after is not None:
+            raise TypeError('`owners_after` must be a list instance or None')
+
         self.fulfillment = fulfillment
         # TODO: Not sure if we should validate for value here
         self.amount = amount
-
-        if not isinstance(owners_after, list) and owners_after is not None:
-            raise TypeError('`owners_after` must be a list instance or None')
-        else:
-            self.owners_after = owners_after
+        self.owners_after = owners_after
 
     def __eq__(self, other):
         # TODO: If `other !== Condition` return `False`
@@ -268,7 +273,7 @@ class Condition(object):
         return cond
 
     @classmethod
-    def generate(cls, owners_after):
+    def generate(cls, owners_after, amount):
         """Generates a Condition from a specifically formed tuple or list.
 
             Note:
@@ -278,34 +283,24 @@ class Condition(object):
 
                 [(address|condition)*, [(address|condition)*, ...], ...]
 
-                If however, the thresholds of individual threshold conditions
-                to be created have to be set specifically, a tuple of the
-                following structure is necessary:
-
-                ([(address|condition)*,
-                  ([(address|condition)*, ...], subthreshold),
-                  ...], threshold)
-
             Args:
-                owners_after (:obj:`list` of :obj:`str`|tuple): The users that
-                    should be able to fulfill the Condition that is being
-                    created.
+                owners_after (:obj:`list` of :obj:`str`): The public key of
+                    the users that should be able to fulfill the Condition
+                    that is being created.
+                amount (:obj:`int`): The amount locked by the condition.
 
             Returns:
                 A Condition that can be used in a Transaction.
 
-            Returns:
+            Raises:
                 TypeError: If `owners_after` is not an instance of `list`.
-                TypeError: If `owners_after` is an empty list.
+                ValueError: If `owners_after` is an empty list.
         """
-        # TODO: We probably want to remove the tuple logic for weights here
-        # again:
-        # github.com/bigchaindb/bigchaindb/issues/730#issuecomment-255144756
-        if isinstance(owners_after, tuple):
-            owners_after, threshold = owners_after
-        else:
-            threshold = len(owners_after)
-
+        threshold = len(owners_after)
+        if not isinstance(amount, int):
+            raise TypeError('`amount` must be a int')
+        if amount < 1:
+            raise AmountError('`amount` needs to be greater than zero')
         if not isinstance(owners_after, list):
             raise TypeError('`owners_after` must be an instance of list')
         if len(owners_after) == 0:
@@ -316,12 +311,12 @@ class Condition(object):
                 ffill = Ed25519Fulfillment(public_key=owners_after[0])
             except TypeError:
                 ffill = owners_after[0]
-            return cls(ffill, owners_after)
+            return cls(ffill, owners_after, amount=amount)
         else:
             initial_cond = ThresholdSha256Fulfillment(threshold=threshold)
             threshold_cond = reduce(cls._gen_condition, owners_after,
                                     initial_cond)
-            return cls(threshold_cond, owners_after)
+            return cls(threshold_cond, owners_after, amount=amount)
 
     @classmethod
     def _gen_condition(cls, initial, current):
@@ -341,14 +336,11 @@ class Condition(object):
             Returns:
                 :class:`cryptoconditions.ThresholdSha256Fulfillment`:
         """
-        if isinstance(current, tuple):
-            owners_after, threshold = current
-        else:
-            owners_after = current
-            try:
-                threshold = len(owners_after)
-            except TypeError:
-                threshold = None
+        owners_after = current
+        try:
+            threshold = len(owners_after)
+        except TypeError:
+            threshold = None
 
         if isinstance(owners_after, list) and len(owners_after) > 1:
             ffill = ThresholdSha256Fulfillment(threshold=threshold)
@@ -423,7 +415,7 @@ class Asset(object):
         self.updatable = updatable
         self.refillable = refillable
 
-        self._validate_asset()
+        self.validate_asset()
 
     def __eq__(self, other):
         try:
@@ -466,7 +458,38 @@ class Asset(object):
         """Generates a unqiue uuid for an Asset"""
         return str(uuid4())
 
-    def _validate_asset(self):
+    @staticmethod
+    def get_asset_id(transactions):
+        """Get the asset id from a list of transaction ids.
+
+        This is useful when we want to check if the multiple inputs of a
+        transaction are related to the same asset id.
+
+        Args:
+            transactions (:obj:`list` of :class:`~bigchaindb.common.
+                transaction.Transaction`): list of transaction usually inputs
+                that should have a matching asset_id
+
+        Returns:
+            str: uuid of the asset.
+
+        Raises:
+            AssetIdMismatch: If the inputs are related to different assets.
+        """
+
+        if not isinstance(transactions, list):
+            transactions = [transactions]
+
+        # create a set of asset_ids
+        asset_ids = {tx.asset.data_id for tx in transactions}
+
+        # check that all the transasctions have the same asset_id
+        if len(asset_ids) > 1:
+            raise AssetIdMismatch(('All inputs of all transactions passed'
+                                   ' need to have the same asset id'))
+        return asset_ids.pop()
+
+    def validate_asset(self, amount=None):
         """Validates the asset"""
         if self.data is not None and not isinstance(self.data, dict):
             raise TypeError('`data` must be a dict instance or None')
@@ -477,6 +500,77 @@ class Asset(object):
         if not isinstance(self.updatable, bool):
             raise TypeError('`updatable` must be a boolean')
 
+        if self.refillable:
+            raise NotImplementedError('Refillable assets are not yet'
+                                      ' implemented')
+        if self.updatable:
+            raise NotImplementedError('Updatable assets are not yet'
+                                      ' implemented')
+
+        # If the amount is supplied we can perform extra validations to
+        # the asset
+        if amount is not None:
+            if not isinstance(amount, int):
+                raise TypeError('`amount` must be an int')
+
+            if self.divisible is False and amount != 1:
+                raise AmountError('non divisible assets always have'
+                                  ' amount equal to one')
+
+            # Since refillable assets are not yet implemented this should
+            # raise and exception
+            if self.divisible is True and amount < 2:
+                raise AmountError('divisible assets must have an amount'
+                                  ' greater than one')
+
+
+class AssetLink(Asset):
+    """An object for unidirectional linking to a Asset.
+    """
+
+    def __init__(self, data_id=None):
+        """Used to point to a specific Asset.
+
+            Args:
+                data_id (str): A Asset to link to.
+        """
+        self.data_id = data_id
+
+    def __bool__(self):
+        return self.data_id is not None
+
+    def __eq__(self, other):
+        return isinstance(other, AssetLink) and \
+                self.to_dict() == self.to_dict()
+
+    @classmethod
+    def from_dict(cls, link):
+        """Transforms a Python dictionary to a AssetLink object.
+
+            Args:
+                link (dict): The link to be transformed.
+
+            Returns:
+                :class:`~bigchaindb.common.transaction.AssetLink`
+        """
+        try:
+            return cls(link['id'])
+        except TypeError:
+            return cls()
+
+    def to_dict(self):
+        """Transforms the object to a Python dictionary.
+
+            Returns:
+                (dict|None): The link as an alternative serialization format.
+        """
+        if self.data_id is None:
+            return None
+        else:
+            return {
+                'id': self.data_id
+            }
+
 
 class Metadata(object):
     """Metadata is used to store a dictionary and its hash in a Transaction."""
@@ -493,16 +587,12 @@ class Metadata(object):
                 data_id (str): A hash corresponding to the contents of
                     `data`.
         """
-        # TODO: Rename `payload_id` to `id`
-        if data_id is not None:
-            self.data_id = data_id
-        else:
-            self.data_id = self.to_hash()
-
         if data is not None and not isinstance(data, dict):
             raise TypeError('`data` must be a dict instance or None')
-        else:
-            self.data = data
+
+        # TODO: Rename `payload_id` to `id`
+        self.data_id = data_id if data_id is not None else self.to_hash()
+        self.data = data
 
     def __eq__(self, other):
         # TODO: If `other !== Data` return `False`
@@ -592,55 +682,44 @@ class Transaction(object):
                 version (int): Defines the version number of a Transaction.
 
         """
-        if version is not None:
-            self.version = version
-        else:
-            self.version = self.__class__.VERSION
-
-        if timestamp is not None:
-            self.timestamp = timestamp
-        else:
-            self.timestamp = gen_timestamp()
-
         if operation not in Transaction.ALLOWED_OPERATIONS:
             allowed_ops = ', '.join(self.__class__.ALLOWED_OPERATIONS)
             raise ValueError('`operation` must be one of {}'
                              .format(allowed_ops))
-        else:
-            self.operation = operation
 
-        # If an asset is not defined in a `CREATE` transaction, create a
-        # default one.
-        if asset is None and operation == Transaction.CREATE:
-            asset = Asset()
-
-        if not isinstance(asset, Asset):
+        # Only assets for 'CREATE' operations can be un-defined.
+        if (asset and not isinstance(asset, Asset) or
+                not asset and operation != Transaction.CREATE):
             raise TypeError('`asset` must be an Asset instance')
-        else:
-            self.asset = asset
 
-        if conditions is not None and not isinstance(conditions, list):
+        if conditions and not isinstance(conditions, list):
             raise TypeError('`conditions` must be a list instance or None')
-        elif conditions is None:
-            self.conditions = []
-        else:
-            self.conditions = conditions
 
-        if fulfillments is not None and not isinstance(fulfillments, list):
+        if fulfillments and not isinstance(fulfillments, list):
             raise TypeError('`fulfillments` must be a list instance or None')
-        elif fulfillments is None:
-            self.fulfillments = []
-        else:
-            self.fulfillments = fulfillments
 
         if metadata is not None and not isinstance(metadata, Metadata):
             raise TypeError('`metadata` must be a Metadata instance or None')
-        else:
-            self.metadata = metadata
+
+        self.version = version if version is not None else self.VERSION
+        self.timestamp = timestamp if timestamp else gen_timestamp()
+        self.operation = operation
+        self.asset = asset if asset else Asset()
+        self.conditions = conditions if conditions else []
+        self.fulfillments = fulfillments if fulfillments else []
+        self.metadata = metadata
+
+        # validate asset
+        # we know that each transaction relates to a single asset
+        # we can sum the amount of all the conditions
+        # for transactions other then CREATE we only have an id so there is
+        # nothing we can validate
+        if self.operation == self.CREATE:
+            amount = sum([condition.amount for condition in self.conditions])
+            self.asset.validate_asset(amount=amount)
 
     @classmethod
-    def create(cls, owners_before, owners_after, metadata=None, asset=None,
-               secret=None, time_expire=None):
+    def create(cls, owners_before, owners_after, metadata=None, asset=None):
         """A simple way to generate a `CREATE` transaction.
 
             Note:
@@ -648,7 +727,6 @@ class Transaction(object):
                 use cases:
                     - Ed25519
                     - ThresholdSha256
-                    - PreimageSha256.
 
                 Additionally, it provides support for the following BigchainDB
                 use cases:
@@ -663,10 +741,6 @@ class Transaction(object):
                     Transaction.
                 asset (:class:`~bigchaindb.common.transaction.Asset`): An Asset
                     to be created in this Transaction.
-                secret (binarystr, optional): A secret string to create a hash-
-                    lock Condition.
-                time_expire (int, optional): The UNIX time a Transaction is
-                    valid.
 
             Returns:
                 :class:`~bigchaindb.common.transaction.Transaction`
@@ -675,54 +749,28 @@ class Transaction(object):
             raise TypeError('`owners_before` must be a list instance')
         if not isinstance(owners_after, list):
             raise TypeError('`owners_after` must be a list instance')
+        if len(owners_before) == 0:
+            raise ValueError('`owners_before` list cannot be empty')
+        if len(owners_after) == 0:
+            raise ValueError('`owners_after` list cannot be empty')
 
         metadata = Metadata(metadata)
-        if len(owners_before) == len(owners_after) and len(owners_after) == 1:
-            # NOTE: Standard case, one owner before, one after.
-            # NOTE: For this case its sufficient to use the same
-            #       fulfillment for the fulfillment and condition.
-            ffill = Ed25519Fulfillment(public_key=owners_before[0])
-            ffill_tx = Fulfillment(ffill, owners_before)
-            cond_tx = Condition.generate(owners_after)
-            return cls(cls.CREATE, asset, [ffill_tx], [cond_tx], metadata)
+        fulfillments = []
+        conditions = []
 
-        elif len(owners_before) == len(owners_after) and len(owners_after) > 1:
-            raise NotImplementedError('Multiple inputs and outputs not'
-                                      'available for CREATE')
-            # NOTE: Multiple inputs and outputs case. Currently not supported.
-            ffills = [Fulfillment(Ed25519Fulfillment(public_key=owner_before),
-                                  [owner_before])
-                      for owner_before in owners_before]
-            conds = [Condition.generate(owners) for owners in owners_after]
-            return cls(cls.CREATE, asset, ffills, conds, metadata)
+        # generate_conditions
+        for owner_after in owners_after:
+            if not isinstance(owner_after, tuple) or len(owner_after) != 2:
+                raise ValueError(('Each `owner_after` in the list must be a'
+                                  ' tuple of `([<list of public keys>],'
+                                  ' <amount>)`'))
+            pub_keys, amount = owner_after
+            conditions.append(Condition.generate(pub_keys, amount))
 
-        elif len(owners_before) == 1 and len(owners_after) > 1:
-            # NOTE: Multiple owners case
-            cond_tx = Condition.generate(owners_after)
-            ffill = Ed25519Fulfillment(public_key=owners_before[0])
-            ffill_tx = Fulfillment(ffill, owners_before)
-            return cls(cls.CREATE, asset, [ffill_tx], [cond_tx], metadata)
+        # generate fulfillments
+        fulfillments.append(Fulfillment.generate(owners_before))
 
-        elif (len(owners_before) == 1 and len(owners_after) == 0 and
-              secret is not None):
-            # NOTE: Hashlock condition case
-            hashlock = PreimageSha256Fulfillment(preimage=secret)
-            cond_tx = Condition(hashlock.condition_uri)
-            ffill = Ed25519Fulfillment(public_key=owners_before[0])
-            ffill_tx = Fulfillment(ffill, owners_before)
-            return cls(cls.CREATE, asset, [ffill_tx], [cond_tx], metadata)
-
-        elif (len(owners_before) > 0 and len(owners_after) == 0 and
-              time_expire is not None):
-            raise NotImplementedError('Timeout conditions will be implemented '
-                                      'later')
-
-        elif (len(owners_before) > 0 and len(owners_after) == 0 and
-              secret is None):
-            raise ValueError('Define a secret to create a hashlock condition')
-
-        else:
-            raise ValueError("These are not the cases you're looking for ;)")
+        return cls(cls.CREATE, asset, fulfillments, conditions, metadata)
 
     @classmethod
     def transfer(cls, inputs, owners_after, asset, metadata=None):
@@ -769,17 +817,17 @@ class Transaction(object):
             raise ValueError('`inputs` must contain at least one item')
         if not isinstance(owners_after, list):
             raise TypeError('`owners_after` must be a list instance')
+        if len(owners_after) == 0:
+            raise ValueError('`owners_after` list cannot be empty')
 
-        # NOTE: See doc strings `Note` for description.
-        if len(inputs) == len(owners_after):
-            if len(owners_after) == 1:
-                conditions = [Condition.generate(owners_after)]
-            elif len(owners_after) > 1:
-                conditions = [Condition.generate(owners) for owners
-                              in owners_after]
-        else:
-            raise ValueError("`inputs` and `owners_after`'s count must be the "
-                             "same")
+        conditions = []
+        for owner_after in owners_after:
+            if not isinstance(owner_after, tuple) or len(owner_after) != 2:
+                raise ValueError(('Each `owner_after` in the list must be a'
+                                  ' tuple of `([<list of public keys>],'
+                                  ' <amount>)`'))
+            pub_keys, amount = owner_after
+            conditions.append(Condition.generate(pub_keys, amount))
 
         metadata = Metadata(metadata)
         inputs = deepcopy(inputs)
@@ -812,20 +860,14 @@ class Transaction(object):
                 :obj:`list` of :class:`~bigchaindb.common.transaction.
                     Fulfillment`
         """
-        inputs = []
-        if condition_indices is None or len(condition_indices) == 0:
-            # NOTE: If no condition indices are passed, we just assume to
-            #       take all conditions as inputs.
-            condition_indices = [index for index, _
-                                 in enumerate(self.conditions)]
-
-        for cid in condition_indices:
-            input_cond = self.conditions[cid]
-            ffill = Fulfillment(input_cond.fulfillment,
-                                input_cond.owners_after,
-                                TransactionLink(self.id, cid))
-            inputs.append(ffill)
-        return inputs
+        # NOTE: If no condition indices are passed, we just assume to
+        #       take all conditions as inputs.
+        return [
+            Fulfillment(self.conditions[cid].fulfillment,
+                        self.conditions[cid].owners_after,
+                        TransactionLink(self.id, cid))
+            for cid in condition_indices or range(len(self.conditions))
+        ]
 
     def add_fulfillment(self, fulfillment):
         """Adds a Fulfillment to a Transaction's list of Fulfillments.
@@ -894,13 +936,12 @@ class Transaction(object):
         key_pairs = {gen_public_key(SigningKey(private_key)):
                      SigningKey(private_key) for private_key in private_keys}
 
-        zippedIO = enumerate(zip(self.fulfillments, self.conditions))
-        for index, (fulfillment, condition) in zippedIO:
+        for index, fulfillment in enumerate(self.fulfillments):
             # NOTE: We clone the current transaction but only add the condition
             #       and fulfillment we're currently working on plus all
             #       previously signed ones.
             tx_partial = Transaction(self.operation, self.asset, [fulfillment],
-                                     [condition], self.metadata,
+                                     self.conditions, self.metadata,
                                      self.timestamp, self.version)
 
             tx_partial_dict = tx_partial.to_dict()
@@ -1057,14 +1098,13 @@ class Transaction(object):
         """
         input_condition_uris_count = len(input_condition_uris)
         fulfillments_count = len(self.fulfillments)
-        conditions_count = len(self.conditions)
 
         def gen_tx(fulfillment, condition, input_condition_uri=None):
             """Splits multiple IO Transactions into partial single IO
             Transactions.
             """
             tx = Transaction(self.operation, self.asset, [fulfillment],
-                             [condition], self.metadata, self.timestamp,
+                             self.conditions, self.metadata, self.timestamp,
                              self.version)
             tx_dict = tx.to_dict()
             tx_dict = Transaction._remove_signatures(tx_dict)
@@ -1075,14 +1115,13 @@ class Transaction(object):
                                                   tx_serialized,
                                                   input_condition_uri)
 
-        if not fulfillments_count == conditions_count == \
-           input_condition_uris_count:
-            raise ValueError('Fulfillments, conditions and '
+        if not fulfillments_count == input_condition_uris_count:
+            raise ValueError('Fulfillments and '
                              'input_condition_uris must have the same count')
-        else:
-            partial_transactions = map(gen_tx, self.fulfillments,
-                                       self.conditions, input_condition_uris)
-            return all(partial_transactions)
+
+        partial_transactions = map(gen_tx, self.fulfillments,
+                                   self.conditions, input_condition_uris)
+        return all(partial_transactions)
 
     @staticmethod
     def _fulfillment_valid(fulfillment, operation, tx_serialized,
@@ -1240,7 +1279,10 @@ class Transaction(object):
             conditions = [Condition.from_dict(condition) for condition
                           in tx['conditions']]
             metadata = Metadata.from_dict(tx['metadata'])
-            asset = Asset.from_dict(tx['asset'])
+            if tx['operation'] in [cls.CREATE, cls.GENESIS]:
+                asset = Asset.from_dict(tx['asset'])
+            else:
+                asset = AssetLink.from_dict(tx['asset'])
 
             return cls(tx['operation'], asset, fulfillments, conditions,
                        metadata, tx['timestamp'], tx_body['version'])
diff --git a/bigchaindb/config_utils.py b/bigchaindb/config_utils.py
index 3b571835..e678f4e9 100644
--- a/bigchaindb/config_utils.py
+++ b/bigchaindb/config_utils.py
@@ -6,7 +6,7 @@ determined according to the following rules:
 * If it's set by an environment variable, then use that value
 * Otherwise, if it's set in a local config file, then use that
   value
-* Otherwise, use the default value (contained in 
+* Otherwise, use the default value (contained in
   ``bigchaindb.__init__``)
 """
 
diff --git a/bigchaindb/core.py b/bigchaindb/core.py
index a5ec25e0..8045e6ba 100644
--- a/bigchaindb/core.py
+++ b/bigchaindb/core.py
@@ -6,13 +6,11 @@ from time import time
 from itertools import compress
 from bigchaindb.common import crypto, exceptions
 from bigchaindb.common.util import gen_timestamp, serialize
-from bigchaindb.common.transaction import TransactionLink, Metadata
-
-import rethinkdb as r
+from bigchaindb.common.transaction import TransactionLink, Asset
 
 import bigchaindb
 
-from bigchaindb.db.utils import Connection
+from bigchaindb.db.utils import Connection, get_backend
 from bigchaindb import config_utils, util
 from bigchaindb.consensus import BaseConsensusRules
 from bigchaindb.models import Block, Transaction
@@ -33,7 +31,7 @@ class Bigchain(object):
     # return if transaction is in backlog
     TX_IN_BACKLOG = 'backlog'
 
-    def __init__(self, host=None, port=None, dbname=None,
+    def __init__(self, host=None, port=None, dbname=None, backend=None,
                  public_key=None, private_key=None, keyring=[],
                  backlog_reassign_delay=None):
         """Initialize the Bigchain instance
@@ -51,6 +49,8 @@ class Bigchain(object):
             host (str): hostname where RethinkDB is running.
             port (int): port in which RethinkDB is running (usually 28015).
             dbname (str): the name of the database to connect to (usually bigchain).
+            backend (:class:`~bigchaindb.db.backends.rethinkdb.RehinkDBBackend`):
+                the database backend to use.
             public_key (str): the base58 encoded public key for the ED25519 curve.
             private_key (str): the base58 encoded private key for the ED25519 curve.
             keyring (list[str]): list of base58 encoded public keys of the federation nodes.
@@ -60,6 +60,7 @@ class Bigchain(object):
         self.host = host or bigchaindb.config['database']['host']
         self.port = port or bigchaindb.config['database']['port']
         self.dbname = dbname or bigchaindb.config['database']['name']
+        self.backend = backend or get_backend(host, port, dbname)
         self.me = public_key or bigchaindb.config['keypair']['public']
         self.me_private = private_key or bigchaindb.config['keypair']['private']
         self.nodes_except_me = keyring or bigchaindb.config['keyring']
@@ -73,9 +74,6 @@ class Bigchain(object):
 
         self.connection = Connection(host=self.host, port=self.port, db=self.dbname)
 
-    def reconnect(self):
-        return r.connect(host=self.host, port=self.port, db=self.dbname)
-
     def write_transaction(self, signed_transaction, durability='soft'):
         """Write the transaction to bigchain.
 
@@ -102,12 +100,9 @@ class Bigchain(object):
         signed_transaction.update({'assignment_timestamp': time()})
 
         # write to the backlog
-        response = self.connection.run(
-                r.table('backlog')
-                .insert(signed_transaction, durability=durability))
-        return response
+        return self.backend.write_transaction(signed_transaction)
 
-    def reassign_transaction(self, transaction, durability='hard'):
+    def reassign_transaction(self, transaction):
         """Assign a transaction to a new node
 
         Args:
@@ -131,23 +126,30 @@ class Bigchain(object):
             # There is no other node to assign to
             new_assignee = self.me
 
-        response = self.connection.run(
-                r.table('backlog')
-                .get(transaction['id'])
-                .update({'assignee': new_assignee, 'assignment_timestamp': time()},
-                        durability=durability))
-        return response
+        return self.backend.update_transaction(
+                transaction['id'],
+                {'assignee': new_assignee, 'assignment_timestamp': time()})
+
+    def delete_transaction(self, *transaction_id):
+        """Delete a transaction from the backlog.
+
+        Args:
+            *transaction_id (str): the transaction(s) to delete
+
+        Returns:
+            The database response.
+        """
+
+        return self.backend.delete_transaction(*transaction_id)
 
     def get_stale_transactions(self):
-        """Get a RethinkDB cursor of stale transactions
+        """Get a cursor of stale transactions.
 
         Transactions are considered stale if they have been assigned a node, but are still in the
         backlog after some amount of time specified in the configuration
         """
 
-        return self.connection.run(
-                r.table('backlog')
-                .filter(lambda tx: time() - tx['assignment_timestamp'] > self.backlog_reassign_delay))
+        return self.backend.get_stale_transactions(self.backlog_reassign_delay)
 
     def validate_transaction(self, transaction):
         """Validate a transaction.
@@ -180,26 +182,55 @@ class Bigchain(object):
 
         try:
             return self.validate_transaction(transaction)
-        except (ValueError, exceptions.OperationError, exceptions.TransactionDoesNotExist,
+        except (ValueError, exceptions.OperationError,
+                exceptions.TransactionDoesNotExist,
                 exceptions.TransactionOwnerError, exceptions.DoubleSpend,
                 exceptions.InvalidHash, exceptions.InvalidSignature,
-                exceptions.TransactionNotInValidBlock):
+                exceptions.TransactionNotInValidBlock, exceptions.AmountError):
             return False
 
-    def get_transaction(self, txid, include_status=False):
-        """Retrieve a transaction with `txid` from bigchain.
+    def get_block(self, block_id, include_status=False):
+        """Get the block with the specified `block_id` (and optionally its status)
 
-        Queries the bigchain for a transaction, if it's in a valid or invalid
-        block.
+        Returns the block corresponding to `block_id` or None if no match is
+        found.
 
         Args:
-            txid (str): transaction id of the transaction to query
+            block_id (str): transaction id of the transaction to get
+            include_status (bool): also return the status of the block
+                       the return value is then a tuple: (block, status)
+        """
+        block = self.backend.get_block(block_id)
+        status = None
+
+        if include_status:
+            if block:
+                status = self.block_election_status(block_id,
+                                                    block['block']['voters'])
+            return block, status
+        else:
+            return block
+
+    def get_transaction(self, txid, include_status=False):
+        """Get the transaction with the specified `txid` (and optionally its status)
+
+        This query begins by looking in the bigchain table for all blocks containing
+        a transaction with the specified `txid`. If one of those blocks is valid, it
+        returns the matching transaction from that block. Else if some of those
+        blocks are undecided, it returns a matching transaction from one of them. If
+        the transaction was found in invalid blocks only, or in no blocks, then this
+        query looks for a matching transaction in the backlog table, and if it finds
+        one there, it returns that.
+
+        Args:
+            txid (str): transaction id of the transaction to get
             include_status (bool): also return the status of the transaction
                                    the return value is then a tuple: (tx, status)
 
         Returns:
             A :class:`~.models.Transaction` instance if the transaction
-            was found, otherwise ``None``.
+            was found in a valid block, an undecided block, or the backlog table,
+            otherwise ``None``.
             If :attr:`include_status` is ``True``, also returns the
             transaction's status if the transaction was found.
         """
@@ -207,36 +238,33 @@ class Bigchain(object):
         response, tx_status = None, None
 
         validity = self.get_blocks_status_containing_tx(txid)
+        check_backlog = True
 
         if validity:
             # Disregard invalid blocks, and return if there are no valid or undecided blocks
             validity = {_id: status for _id, status in validity.items()
-                                    if status != Bigchain.BLOCK_INVALID}
+                        if status != Bigchain.BLOCK_INVALID}
             if validity:
 
+                # The transaction _was_ found in an undecided or valid block,
+                # so there's no need to look in the backlog table
+                check_backlog = False
+
                 tx_status = self.TX_UNDECIDED
                 # If the transaction is in a valid or any undecided block, return it. Does not check
-                # if transactions in undecided blocks are consistent, but selects the valid block before
-                # undecided ones
+                # if transactions in undecided blocks are consistent, but selects the valid block
+                # before undecided ones
                 for target_block_id in validity:
                     if validity[target_block_id] == Bigchain.BLOCK_VALID:
                         tx_status = self.TX_VALID
                         break
 
                 # Query the transaction in the target block and return
-                response = self.connection.run(
-                        r.table('bigchain', read_mode=self.read_mode)
-                        .get(target_block_id)
-                        .get_field('block')
-                        .get_field('transactions')
-                        .filter(lambda tx: tx['id'] == txid))[0]
+                response = self.backend.get_transaction_from_block(txid, target_block_id)
+
+        if check_backlog:
+            response = self.backend.get_transaction_from_backlog(txid)
 
-        else:
-            # Otherwise, check the backlog
-            response = self.connection.run(r.table('backlog')
-                                           .get(txid)
-                                           .without('assignee', 'assignment_timestamp')
-                                           .default(None))
             if response:
                 tx_status = self.TX_IN_BACKLOG
 
@@ -262,24 +290,6 @@ class Bigchain(object):
         _, status = self.get_transaction(txid, include_status=True)
         return status
 
-    def search_block_election_on_index(self, value, index):
-        """Retrieve block election information given a secondary index and value
-
-        Args:
-            value: a value to search (e.g. transaction id string, payload hash string)
-            index (str): name of a secondary index, e.g. 'transaction_id'
-
-        Returns:
-            :obj:`list` of :obj:`dict`: A list of blocks with with only election information
-        """
-        # First, get information on all blocks which contain this transaction
-        response = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)
-                .get_all(value, index=index)
-                .pluck('votes', 'id', {'block': ['voters']}))
-
-        return list(response)
-
     def get_blocks_status_containing_tx(self, txid):
         """Retrieve block ids and statuses related to a transaction
 
@@ -294,7 +304,7 @@ class Bigchain(object):
         """
 
         # First, get information on all blocks which contain this transaction
-        blocks = self.search_block_election_on_index(txid, 'transaction_id')
+        blocks = self.backend.get_blocks_status_from_transaction(txid)
         if blocks:
             # Determine the election status of each block
             validity = {
@@ -305,7 +315,7 @@ class Bigchain(object):
             }
 
             # NOTE: If there are multiple valid blocks with this transaction,
-            #       something has gone wrong
+            # something has gone wrong
             if list(validity.values()).count(Bigchain.BLOCK_VALID) > 1:
                 block_ids = str([block for block in validity
                                  if validity[block] == Bigchain.BLOCK_VALID])
@@ -336,14 +346,8 @@ class Bigchain(object):
             A list of transactions containing that metadata. If no transaction exists with that metadata it
             returns an empty list `[]`
         """
-        cursor = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)
-                .get_all(metadata_id, index='metadata_id')
-                .concat_map(lambda block: block['block']['transactions'])
-                .filter(lambda transaction: transaction['transaction']['metadata']['id'] == metadata_id))
-
-        transactions = list(cursor)
-        return [Transaction.from_dict(tx) for tx in transactions]
+        cursor = self.backend.get_transactions_by_metadata_id(metadata_id)
+        return [Transaction.from_dict(tx) for tx in cursor]
 
     def get_txs_by_asset_id(self, asset_id):
         """Retrieves transactions related to a particular asset.
@@ -358,14 +362,25 @@ class Bigchain(object):
             A list of transactions containing related to the asset. If no transaction exists for that asset it
             returns an empty list `[]`
         """
-        cursor = self.connection.run(
-            r.table('bigchain', read_mode=self.read_mode)
-             .get_all(asset_id, index='asset_id')
-             .concat_map(lambda block: block['block']['transactions'])
-             .filter(lambda transaction: transaction['transaction']['asset']['id'] == asset_id))
 
+        cursor = self.backend.get_transactions_by_asset_id(asset_id)
         return [Transaction.from_dict(tx) for tx in cursor]
 
+    def get_asset_by_id(self, asset_id):
+        """Returns the asset associated with an asset_id.
+
+            Args:
+                asset_id (str): The asset id.
+
+            Returns:
+                :class:`~bigchaindb.common.transaction.Asset` if the asset
+                exists else None.
+        """
+        cursor = self.backend.get_asset_by_id(asset_id)
+        cursor = list(cursor)
+        if cursor:
+            return Asset.from_dict(cursor[0]['transaction']['asset'])
+
     def get_spent(self, txid, cid):
         """Check if a `txid` was already used as an input.
 
@@ -382,13 +397,7 @@ class Bigchain(object):
         """
         # checks if an input was already spent
         # checks if the bigchain has any transaction with input {'txid': ..., 'cid': ...}
-        response = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)
-                .concat_map(lambda doc: doc['block']['transactions'])
-                .filter(lambda transaction: transaction['transaction']['fulfillments']
-                    .contains(lambda fulfillment: fulfillment['input'] == {'txid': txid, 'cid': cid})))
-
-        transactions = list(response)
+        transactions = list(self.backend.get_spent(txid, cid))
 
         # a transaction_id should have been spent at most one time
         if transactions:
@@ -400,8 +409,9 @@ class Bigchain(object):
                 if self.get_transaction(transaction['id']):
                     num_valid_transactions += 1
                 if num_valid_transactions > 1:
-                    raise exceptions.DoubleSpend('`{}` was spent more then once. There is a problem with the chain'.format(
-                        txid))
+                    raise exceptions.DoubleSpend(
+                        '`{}` was spent more then once. There is a problem with the chain'.format(
+                            txid))
 
             if num_valid_transactions:
                 return Transaction.from_dict(transactions[0])
@@ -423,12 +433,7 @@ class Bigchain(object):
         """
 
         # get all transactions in which owner is in the `owners_after` list
-        response = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)
-                .concat_map(lambda doc: doc['block']['transactions'])
-                .filter(lambda tx: tx['transaction']['conditions']
-                    .contains(lambda c: c['owners_after']
-                        .contains(owner))))
+        response = self.backend.get_owned_ids(owner)
         owned = []
 
         for tx in response:
@@ -439,7 +444,7 @@ class Bigchain(object):
                     continue
 
             # NOTE: It's OK to not serialize the transaction here, as we do not
-            #       use it after the execution of this function.
+            # use it after the execution of this function.
             # a transaction can contain multiple outputs (conditions) so we need to iterate over all of them
             # to get a list of outputs available to spend
             for index, cond in enumerate(tx['transaction']['conditions']):
@@ -513,9 +518,7 @@ class Bigchain(object):
                 but the vote is invalid.
 
         """
-        votes = list(self.connection.run(
-            r.table('votes', read_mode=self.read_mode)
-            .get_all([block_id, self.me], index='block_and_voter')))
+        votes = list(self.backend.get_votes_by_block_id_and_voter(block_id, self.me))
 
         if len(votes) > 1:
             raise exceptions.MultipleVotesError('Block {block_id} has {n_votes} votes from public key {me}'
@@ -537,21 +540,16 @@ class Bigchain(object):
             block (Block): block to write to bigchain.
         """
 
-        self.connection.run(
-                r.table('bigchain')
-                .insert(r.json(block.to_str()), durability=durability))
+        return self.backend.write_block(block.to_str(), durability=durability)
 
     def transaction_exists(self, transaction_id):
-        response = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)\
-                .get_all(transaction_id, index='transaction_id'))
-        return len(response.items) > 0
+        return self.backend.has_transaction(transaction_id)
 
     def prepare_genesis_block(self):
         """Prepare a genesis block."""
 
         metadata = {'message': 'Hello World from the BigchainDB'}
-        transaction = Transaction.create([self.me], [self.me],
+        transaction = Transaction.create([self.me], [([self.me], 1)],
                                          metadata=metadata)
 
         # NOTE: The transaction model doesn't expose an API to generate a
@@ -574,9 +572,7 @@ class Bigchain(object):
         # 2. create the block with one transaction
         # 3. write the block to the bigchain
 
-        blocks_count = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)
-                .count())
+        blocks_count = self.backend.count_blocks()
 
         if blocks_count:
             raise exceptions.GenesisBlockAlreadyExistsError('Cannot create the Genesis block')
@@ -588,7 +584,7 @@ class Bigchain(object):
 
     def vote(self, block_id, previous_block_id, decision, invalid_reason=None):
         """Create a signed vote for a block given the
-		:attr:`previous_block_id` and the :attr:`decision` (valid/invalid).
+        :attr:`previous_block_id` and the :attr:`decision` (valid/invalid).
 
         Args:
             block_id (str): The id of the block to vote on.
@@ -621,69 +617,12 @@ class Bigchain(object):
 
     def write_vote(self, vote):
         """Write the vote to the database."""
-
-        self.connection.run(
-                r.table('votes')
-                .insert(vote))
+        return self.backend.write_vote(vote)
 
     def get_last_voted_block(self):
         """Returns the last block that this node voted on."""
 
-        try:
-            # get the latest value for the vote timestamp (over all votes)
-            max_timestamp = self.connection.run(
-                    r.table('votes', read_mode=self.read_mode)
-                    .filter(r.row['node_pubkey'] == self.me)
-                    .max(r.row['vote']['timestamp']))['vote']['timestamp']
-
-            last_voted = list(self.connection.run(
-                r.table('votes', read_mode=self.read_mode)
-                .filter(r.row['vote']['timestamp'] == max_timestamp)
-                .filter(r.row['node_pubkey'] == self.me)))
-
-        except r.ReqlNonExistenceError:
-            # return last vote if last vote exists else return Genesis block
-            res = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)
-                .filter(util.is_genesis_block))
-            block = list(res)[0]
-            return Block.from_dict(block)
-
-        # Now the fun starts. Since the resolution of timestamp is a second,
-        # we might have more than one vote per timestamp. If this is the case
-        # then we need to rebuild the chain for the blocks that have been retrieved
-        # to get the last one.
-
-        # Given a block_id, mapping returns the id of the block pointing at it.
-        mapping = {v['vote']['previous_block']: v['vote']['voting_for_block']
-                   for v in last_voted}
-
-        # Since we follow the chain backwards, we can start from a random
-        # point of the chain and "move up" from it.
-        last_block_id = list(mapping.values())[0]
-
-        # We must be sure to break the infinite loop. This happens when:
-        # - the block we are currenty iterating is the one we are looking for.
-        #   This will trigger a KeyError, breaking the loop
-        # - we are visiting again a node we already explored, hence there is
-        #   a loop. This might happen if a vote points both `previous_block`
-        #   and `voting_for_block` to the same `block_id`
-        explored = set()
-
-        while True:
-            try:
-                if last_block_id in explored:
-                    raise exceptions.CyclicBlockchainError()
-                explored.add(last_block_id)
-                last_block_id = mapping[last_block_id]
-            except KeyError:
-                break
-
-        res = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)
-                .get(last_block_id))
-
-        return Block.from_dict(res)
+        return Block.from_dict(self.backend.get_last_voted_block(self.me))
 
     def get_unvoted_blocks(self):
         """Return all the blocks that have not been voted on by this node.
@@ -692,37 +631,26 @@ class Bigchain(object):
             :obj:`list` of :obj:`dict`: a list of unvoted blocks
         """
 
-        unvoted = self.connection.run(
-                r.table('bigchain', read_mode=self.read_mode)
-                .filter(lambda block: r.table('votes', read_mode=self.read_mode)
-                    .get_all([block['id'], self.me], index='block_and_voter')
-                    .is_empty())
-                .order_by(r.asc(r.row['block']['timestamp'])))
-
-        # FIXME: I (@vrde) don't like this solution. Filtering should be done at a
-        #        database level. Solving issue #444 can help untangling the situation
-        unvoted_blocks = filter(lambda block: not util.is_genesis_block(block), unvoted)
-        return unvoted_blocks
+        # XXX: should this return instaces of Block?
+        return self.backend.get_unvoted_blocks(self.me)
 
     def block_election_status(self, block_id, voters):
         """Tally the votes on a block, and return the status: valid, invalid, or undecided."""
 
-        votes = self.connection.run(r.table('votes', read_mode=self.read_mode)
-            .between([block_id, r.minval], [block_id, r.maxval], index='block_and_voter'))
-
-        votes = list(votes)
-
+        votes = list(self.backend.get_votes_by_block_id(block_id))
         n_voters = len(voters)
 
         voter_counts = collections.Counter([vote['node_pubkey'] for vote in votes])
         for node in voter_counts:
             if voter_counts[node] > 1:
-                raise exceptions.MultipleVotesError('Block {block_id} has multiple votes ({n_votes}) from voting node {node_id}'
-                                                    .format(block_id=block_id, n_votes=str(voter_counts[node]), node_id=node))
+                raise exceptions.MultipleVotesError(
+                    'Block {block_id} has multiple votes ({n_votes}) from voting node {node_id}'
+                    .format(block_id=block_id, n_votes=str(voter_counts[node]), node_id=node))
 
         if len(votes) > n_voters:
             raise exceptions.MultipleVotesError('Block {block_id} has {n_votes} votes cast, but only {n_voters} voters'
-                                                .format(block_id=block_id, n_votes=str(len(votes)), n_voters=str(n_voters)))
+                                                .format(block_id=block_id, n_votes=str(len(votes)),
+                                                        n_voters=str(n_voters)))
 
         # vote_cast is the list of votes e.g. [True, True, False]
         vote_cast = [vote['vote']['is_block_valid'] for vote in votes]
diff --git a/bigchaindb/db/__init__.py b/bigchaindb/db/__init__.py
index 9c299f48..28ebfc3a 100644
--- a/bigchaindb/db/__init__.py
+++ b/bigchaindb/db/__init__.py
@@ -1,2 +1,2 @@
 # TODO can we use explicit imports?
-from bigchaindb.db.utils import *
+from bigchaindb.db.utils import *  # noqa: F401,F403
diff --git a/bigchaindb/db/backends/__init__.py b/bigchaindb/db/backends/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/bigchaindb/db/backends/rethinkdb.py b/bigchaindb/db/backends/rethinkdb.py
new file mode 100644
index 00000000..b9355b41
--- /dev/null
+++ b/bigchaindb/db/backends/rethinkdb.py
@@ -0,0 +1,431 @@
+"""Backend implementation for RethinkDB.
+
+This module contains all the methods to store and retrieve data from RethinkDB.
+"""
+
+from time import time
+
+import rethinkdb as r
+
+from bigchaindb import util
+from bigchaindb.db.utils import Connection
+from bigchaindb.common import exceptions
+
+
+class RethinkDBBackend:
+
+    def __init__(self, host=None, port=None, db=None):
+        """Initialize a new RethinkDB Backend instance.
+
+        Args:
+            host (str): the host to connect to.
+            port (int): the port to connect to.
+            db (str): the name of the database to use.
+        """
+
+        self.read_mode = 'majority'
+        self.durability = 'soft'
+        self.connection = Connection(host=host, port=port, db=db)
+
+    def write_transaction(self, signed_transaction):
+        """Write a transaction to the backlog table.
+
+        Args:
+            signed_transaction (dict): a signed transaction.
+
+        Returns:
+            The result of the operation.
+        """
+
+        return self.connection.run(
+                r.table('backlog')
+                .insert(signed_transaction, durability=self.durability))
+
+    def update_transaction(self, transaction_id, doc):
+        """Update a transaction in the backlog table.
+
+        Args:
+            transaction_id (str): the id of the transaction.
+            doc (dict): the values to update.
+
+        Returns:
+            The result of the operation.
+        """
+
+        return self.connection.run(
+                r.table('backlog')
+                .get(transaction_id)
+                .update(doc))
+
+    def delete_transaction(self, *transaction_id):
+        """Delete a transaction from the backlog.
+
+        Args:
+            *transaction_id (str): the transaction(s) to delete
+
+        Returns:
+            The database response.
+        """
+
+        return self.connection.run(
+                r.table('backlog')
+                .get_all(*transaction_id)
+                .delete(durability='hard'))
+
+    def get_stale_transactions(self, reassign_delay):
+        """Get a cursor of stale transactions.
+
+        Transactions are considered stale if they have been assigned a node,
+        but are still in the backlog after some amount of time specified in the
+        configuration.
+
+        Args:
+            reassign_delay (int): threshold (in seconds) to mark a transaction stale.
+
+        Returns:
+            A cursor of transactions.
+        """
+
+        return self.connection.run(
+                r.table('backlog')
+                .filter(lambda tx: time() - tx['assignment_timestamp'] > reassign_delay))
+
+    def get_transaction_from_block(self, transaction_id, block_id):
+        """Get a transaction from a specific block.
+
+        Args:
+            transaction_id (str): the id of the transaction.
+            block_id (str): the id of the block.
+
+        Returns:
+            The matching transaction.
+        """
+        return self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .get(block_id)
+                .get_field('block')
+                .get_field('transactions')
+                .filter(lambda tx: tx['id'] == transaction_id))[0]
+
+    def get_transaction_from_backlog(self, transaction_id):
+        """Get a transaction from backlog.
+
+        Args:
+            transaction_id (str): the id of the transaction.
+
+        Returns:
+            The matching transaction.
+        """
+        return self.connection.run(
+                r.table('backlog')
+                .get(transaction_id)
+                .without('assignee', 'assignment_timestamp')
+                .default(None))
+
+    def get_blocks_status_from_transaction(self, transaction_id):
+        """Retrieve block election information given a secondary index and value
+
+        Args:
+            value: a value to search (e.g. transaction id string, payload hash string)
+            index (str): name of a secondary index, e.g. 'transaction_id'
+
+        Returns:
+            :obj:`list` of :obj:`dict`: A list of blocks with with only election information
+        """
+
+        return self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .get_all(transaction_id, index='transaction_id')
+                .pluck('votes', 'id', {'block': ['voters']}))
+
+    def get_transactions_by_metadata_id(self, metadata_id):
+        """Retrieves transactions related to a metadata.
+
+        When creating a transaction one of the optional arguments is the `metadata`. The metadata is a generic
+        dict that contains extra information that can be appended to the transaction.
+
+        To make it easy to query the bigchain for that particular metadata we create a UUID for the metadata and
+        store it with the transaction.
+
+        Args:
+            metadata_id (str): the id for this particular metadata.
+
+        Returns:
+            A list of transactions containing that metadata. If no transaction exists with that metadata it
+            returns an empty list `[]`
+        """
+        return self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .get_all(metadata_id, index='metadata_id')
+                .concat_map(lambda block: block['block']['transactions'])
+                .filter(lambda transaction: transaction['transaction']['metadata']['id'] == metadata_id))
+
+    def get_transactions_by_asset_id(self, asset_id):
+        """Retrieves transactions related to a particular asset.
+
+        A digital asset in bigchaindb is identified by an uuid. This allows us to query all the transactions
+        related to a particular digital asset, knowing the id.
+
+        Args:
+            asset_id (str): the id for this particular metadata.
+
+        Returns:
+            A list of transactions containing related to the asset. If no transaction exists for that asset it
+            returns an empty list `[]`
+        """
+
+        return self.connection.run(
+            r.table('bigchain', read_mode=self.read_mode)
+             .get_all(asset_id, index='asset_id')
+             .concat_map(lambda block: block['block']['transactions'])
+             .filter(lambda transaction:
+                     transaction['transaction']['asset']['id'] == asset_id))
+
+    def get_asset_by_id(self, asset_id):
+        """Returns the asset associated with an asset_id.
+
+            Args:
+                asset_id (str): The asset id.
+
+            Returns:
+                Returns a rethinkdb cursor.
+        """
+        return self.connection.run(
+            r.table('bigchain', read_mode=self.read_mode)
+             .get_all(asset_id, index='asset_id')
+             .concat_map(lambda block: block['block']['transactions'])
+             .filter(lambda transaction:
+                     transaction['transaction']['asset']['id'] == asset_id)
+             .filter(lambda transaction:
+                     transaction['transaction']['operation'] == 'CREATE')
+             .pluck({'transaction': 'asset'}))
+
+    def get_spent(self, transaction_id, condition_id):
+        """Check if a `txid` was already used as an input.
+
+        A transaction can be used as an input for another transaction. Bigchain needs to make sure that a
+        given `txid` is only used once.
+
+        Args:
+            transaction_id (str): The id of the transaction.
+            condition_id (int): The index of the condition in the respective transaction.
+
+        Returns:
+            The transaction that used the `txid` as an input else `None`
+        """
+
+        # TODO: use index!
+        return self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .concat_map(lambda doc: doc['block']['transactions'])
+                .filter(lambda transaction: transaction['transaction']['fulfillments'].contains(
+                    lambda fulfillment: fulfillment['input'] == {'txid': transaction_id, 'cid': condition_id})))
+
+    def get_owned_ids(self, owner):
+        """Retrieve a list of `txids` that can we used has inputs.
+
+        Args:
+            owner (str): base58 encoded public key.
+
+        Returns:
+            A cursor for the matching transactions.
+        """
+
+        # TODO: use index!
+        return self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .concat_map(lambda doc: doc['block']['transactions'])
+                .filter(lambda tx: tx['transaction']['conditions'].contains(
+                    lambda c: c['owners_after'].contains(owner))))
+
+    def get_votes_by_block_id(self, block_id):
+        """Get all the votes casted for a specific block.
+
+        Args:
+            block_id (str): the block id to use.
+
+        Returns:
+            A cursor for the matching votes.
+        """
+        return self.connection.run(
+                r.table('votes', read_mode=self.read_mode)
+                .between([block_id, r.minval], [block_id, r.maxval], index='block_and_voter'))
+
+    def get_votes_by_block_id_and_voter(self, block_id, node_pubkey):
+        """Get all the votes casted for a specific block by a specific voter.
+
+        Args:
+            block_id (str): the block id to use.
+            node_pubkey (str): base58 encoded public key
+
+        Returns:
+            A cursor for the matching votes.
+        """
+        return self.connection.run(
+                r.table('votes', read_mode=self.read_mode)
+                .get_all([block_id, node_pubkey], index='block_and_voter'))
+
+    def write_block(self, block, durability='soft'):
+        """Write a block to the bigchain table.
+
+        Args:
+            block (dict): the block to write.
+
+        Returns:
+            The database response.
+        """
+        return self.connection.run(
+                r.table('bigchain')
+                .insert(r.json(block), durability=durability))
+
+    def get_block(self, block_id):
+        """Get a block from the bigchain table
+
+        Args:
+            block_id (str): block id of the block to get
+
+        Returns:
+            block (dict): the block or `None`
+        """
+        return self.connection.run(r.table('bigchain').get(block_id))
+
+    def has_transaction(self, transaction_id):
+        """Check if a transaction exists in the bigchain table.
+
+        Args:
+            transaction_id (str): the id of the transaction to check.
+
+        Returns:
+            ``True`` if the transaction exists, ``False`` otherwise.
+        """
+        return bool(self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .get_all(transaction_id, index='transaction_id').count()))
+
+    def count_blocks(self):
+        """Count the number of blocks in the bigchain table.
+
+        Returns:
+            The number of blocks.
+        """
+
+        return self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .count())
+
+    def count_backlog(self):
+        """Count the number of transactions in the backlog table.
+
+        Returns:
+            The number of transactions in the backlog.
+        """
+
+        return self.connection.run(
+                r.table('backlog', read_mode=self.read_mode)
+                .count())
+
+    def write_vote(self, vote):
+        """Write a vote to the votes table.
+
+        Args:
+            vote (dict): the vote to write.
+
+        Returns:
+            The database response.
+        """
+        return self.connection.run(
+                r.table('votes')
+                .insert(vote))
+
+    def get_genesis_block(self):
+        """Get the genesis block
+
+        Returns:
+            The genesis block
+        """
+        return self.connection.run(
+            r.table('bigchain', read_mode=self.read_mode)
+            .filter(util.is_genesis_block)
+            .nth(0))
+
+    def get_last_voted_block(self, node_pubkey):
+        """Get the last voted block for a specific node.
+
+        Args:
+            node_pubkey (str): base58 encoded public key.
+
+        Returns:
+            The last block the node has voted on. If the node didn't cast
+            any vote then the genesis block is returned.
+        """
+        try:
+            # get the latest value for the vote timestamp (over all votes)
+            max_timestamp = self.connection.run(
+                    r.table('votes', read_mode=self.read_mode)
+                    .filter(r.row['node_pubkey'] == node_pubkey)
+                    .max(r.row['vote']['timestamp']))['vote']['timestamp']
+
+            last_voted = list(self.connection.run(
+                r.table('votes', read_mode=self.read_mode)
+                .filter(r.row['vote']['timestamp'] == max_timestamp)
+                .filter(r.row['node_pubkey'] == node_pubkey)))
+
+        except r.ReqlNonExistenceError:
+            # return last vote if last vote exists else return Genesis block
+            return self.get_genesis_block()
+
+        # Now the fun starts. Since the resolution of timestamp is a second,
+        # we might have more than one vote per timestamp. If this is the case
+        # then we need to rebuild the chain for the blocks that have been retrieved
+        # to get the last one.
+
+        # Given a block_id, mapping returns the id of the block pointing at it.
+        mapping = {v['vote']['previous_block']: v['vote']['voting_for_block']
+                   for v in last_voted}
+
+        # Since we follow the chain backwards, we can start from a random
+        # point of the chain and "move up" from it.
+        last_block_id = list(mapping.values())[0]
+
+        # We must be sure to break the infinite loop. This happens when:
+        # - the block we are currenty iterating is the one we are looking for.
+        #   This will trigger a KeyError, breaking the loop
+        # - we are visiting again a node we already explored, hence there is
+        #   a loop. This might happen if a vote points both `previous_block`
+        #   and `voting_for_block` to the same `block_id`
+        explored = set()
+
+        while True:
+            try:
+                if last_block_id in explored:
+                    raise exceptions.CyclicBlockchainError()
+                explored.add(last_block_id)
+                last_block_id = mapping[last_block_id]
+            except KeyError:
+                break
+
+        return self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .get(last_block_id))
+
+    def get_unvoted_blocks(self, node_pubkey):
+        """Return all the blocks that have not been voted by the specified node.
+
+        Args:
+            node_pubkey (str): base58 encoded public key
+
+        Returns:
+            :obj:`list` of :obj:`dict`: a list of unvoted blocks
+        """
+
+        unvoted = self.connection.run(
+                r.table('bigchain', read_mode=self.read_mode)
+                .filter(lambda block: r.table('votes', read_mode=self.read_mode)
+                                       .get_all([block['id'], node_pubkey], index='block_and_voter')
+                                       .is_empty())
+                .order_by(r.asc(r.row['block']['timestamp'])))
+
+        # FIXME: I (@vrde) don't like this solution. Filtering should be done at a
+        #        database level. Solving issue #444 can help untangling the situation
+        unvoted_blocks = filter(lambda block: not util.is_genesis_block(block), unvoted)
+        return unvoted_blocks
diff --git a/bigchaindb/db/utils.py b/bigchaindb/db/utils.py
index 92e0fdd3..8e34fd99 100644
--- a/bigchaindb/db/utils.py
+++ b/bigchaindb/db/utils.py
@@ -67,6 +67,18 @@ class Connection:
                     time.sleep(2**i)
 
 
+def get_backend(host=None, port=None, db=None):
+    '''Get a backend instance.'''
+
+    from bigchaindb.db.backends import rethinkdb
+
+    # NOTE: this function will be re-implemented when we have real
+    # multiple backends to support. Right now it returns the RethinkDB one.
+    return rethinkdb.RethinkDBBackend(host=host or bigchaindb.config['database']['host'],
+                                      port=port or bigchaindb.config['database']['port'],
+                                      db=db or bigchaindb.config['database']['name'])
+
+
 def get_conn():
     '''Get the connection to the database.'''
 
@@ -149,10 +161,7 @@ def create_votes_secondary_index(conn, dbname):
     r.db(dbname).table('votes').index_wait().run(conn)
 
 
-def init():
-    # Try to access the keypair, throws an exception if it does not exist
-    b = bigchaindb.Bigchain()
-
+def init_database():
     conn = get_conn()
     dbname = get_database_name()
     create_database(conn, dbname)
@@ -160,10 +169,18 @@ def init():
     table_names = ['bigchain', 'backlog', 'votes']
     for table_name in table_names:
         create_table(conn, dbname, table_name)
+
     create_bigchain_secondary_index(conn, dbname)
     create_backlog_secondary_index(conn, dbname)
     create_votes_secondary_index(conn, dbname)
 
+
+def init():
+    # Try to access the keypair, throws an exception if it does not exist
+    b = bigchaindb.Bigchain()
+
+    init_database()
+
     logger.info('Create genesis block.')
     b.create_genesis_block()
     logger.info('Done, have fun!')
@@ -172,9 +189,9 @@ def init():
 def drop(assume_yes=False):
     conn = get_conn()
     dbname = bigchaindb.config['database']['name']
-
     if assume_yes:
         response = 'y'
+
     else:
         response = input('Do you want to drop `{}` database? [y/n]: '.format(dbname))
 
@@ -185,5 +202,6 @@ def drop(assume_yes=False):
             logger.info('Done.')
         except r.ReqlOpFailedError:
             raise exceptions.DatabaseDoesNotExist('Database `{}` does not exist'.format(dbname))
+
     else:
         logger.info('Drop aborted')
diff --git a/bigchaindb/models.py b/bigchaindb/models.py
index 87ea57bb..cd472ed6 100644
--- a/bigchaindb/models.py
+++ b/bigchaindb/models.py
@@ -3,41 +3,11 @@ from bigchaindb.common.exceptions import (InvalidHash, InvalidSignature,
                                           OperationError, DoubleSpend,
                                           TransactionDoesNotExist,
                                           TransactionNotInValidBlock,
-                                          AssetIdMismatch)
+                                          AssetIdMismatch, AmountError)
 from bigchaindb.common.transaction import Transaction, Asset
 from bigchaindb.common.util import gen_timestamp, serialize
 
 
-class Asset(Asset):
-    @staticmethod
-    def get_asset_id(transactions):
-        """Get the asset id from a list of transaction ids.
-
-        This is useful when we want to check if the multiple inputs of a transaction
-        are related to the same asset id.
-
-        Args:
-            transactions (list): list of transaction usually inputs that should have a matching asset_id
-
-        Returns:
-            str: uuid of the asset.
-
-        Raises:
-            AssetIdMismatch: If the inputs are related to different assets.
-        """
-
-        if not isinstance(transactions, list):
-            transactions = [transactions]
-
-        # create a set of asset_ids
-        asset_ids = {tx.asset.data_id for tx in transactions}
-
-        # check that all the transasctions have the same asset_id
-        if len(asset_ids) > 1:
-            raise AssetIdMismatch("All inputs of a transaction need to have the same asset id.")
-        return asset_ids.pop()
-
-
 class Transaction(Transaction):
     def validate(self, bigchain):
         """Validate a transaction.
@@ -73,7 +43,8 @@ class Transaction(Transaction):
             if inputs_defined:
                 raise ValueError('A CREATE operation has no inputs')
             # validate asset
-            self.asset._validate_asset()
+            amount = sum([condition.amount for condition in self.conditions])
+            self.asset.validate_asset(amount=amount)
         elif self.operation == Transaction.TRANSFER:
             if not inputs_defined:
                 raise ValueError('Only `CREATE` transactions can have null '
@@ -81,6 +52,7 @@ class Transaction(Transaction):
             # check inputs
             # store the inputs so that we can check if the asset ids match
             input_txs = []
+            input_amount = 0
             for ffill in self.fulfillments:
                 input_txid = ffill.tx_input.txid
                 input_cid = ffill.tx_input.cid
@@ -103,11 +75,34 @@ class Transaction(Transaction):
 
                 input_conditions.append(input_tx.conditions[input_cid])
                 input_txs.append(input_tx)
+                if input_tx.conditions[input_cid].amount < 1:
+                    raise AmountError('`amount` needs to be greater than zero')
+                input_amount += input_tx.conditions[input_cid].amount
 
             # validate asset id
             asset_id = Asset.get_asset_id(input_txs)
             if asset_id != self.asset.data_id:
-                raise AssetIdMismatch('The asset id of the input does not match the asset id of the transaction')
+                raise AssetIdMismatch(('The asset id of the input does not'
+                                       ' match the asset id of the'
+                                       ' transaction'))
+
+            # get the asset creation to see if its divisible or not
+            asset = bigchain.get_asset_by_id(asset_id)
+            # validate the asset
+            asset.validate_asset(amount=input_amount)
+            # validate the amounts
+            output_amount = 0
+            for condition in self.conditions:
+                if condition.amount < 1:
+                    raise AmountError('`amount` needs to be greater than zero')
+                output_amount += condition.amount
+
+            if output_amount != input_amount:
+                raise AmountError(('The amount used in the inputs `{}`'
+                                   ' needs to be same as the amount used'
+                                   ' in the outputs `{}`')
+                                  .format(input_amount, output_amount))
+
         else:
             allowed_operations = ', '.join(Transaction.ALLOWED_OPERATIONS)
             raise TypeError('`operation`: `{}` must be either {}.'
@@ -120,8 +115,36 @@ class Transaction(Transaction):
 
 
 class Block(object):
+    """Bundle a list of Transactions in a Block. Nodes vote on its validity.
+
+    Attributes:
+        transaction (:obj:`list` of :class:`~.Transaction`):
+            Transactions to be included in the Block.
+        node_pubkey (str): The public key of the node creating the
+            Block.
+        timestamp (str): The Unix time a Block was created.
+        voters (:obj:`list` of :obj:`str`): A list of a federation
+            nodes' public keys supposed to vote on the Block.
+        signature (str): A cryptographic signature ensuring the
+            integrity and validity of the creator of a Block.
+    """
+
     def __init__(self, transactions=None, node_pubkey=None, timestamp=None,
                  voters=None, signature=None):
+        """The Block model is mainly used for (de)serialization and integrity
+        checking.
+
+        Args:
+            transaction (:obj:`list` of :class:`~.Transaction`):
+                Transactions to be included in the Block.
+            node_pubkey (str): The public key of the node creating the
+                Block.
+            timestamp (str): The Unix time a Block was created.
+            voters (:obj:`list` of :obj:`str`): A list of a federation
+                nodes' public keys supposed to vote on the Block.
+            signature (str): A cryptographic signature ensuring the
+                integrity and validity of the creator of a Block.
+        """
         if transactions is not None and not isinstance(transactions, list):
             raise TypeError('`transactions` must be a list instance or None')
         else:
@@ -148,18 +171,20 @@ class Block(object):
         return self.to_dict() == other
 
     def validate(self, bigchain):
-        """Validate a block.
+        """Validate the Block.
 
         Args:
-            bigchain (Bigchain): an instantiated bigchaindb.Bigchain object.
+            bigchain (:class:`~bigchaindb.Bigchain`): An instantiated Bigchain
+                object.
 
         Returns:
-            block (Block): The block as a `Block` object if it is valid.
-                           Else it raises an appropriate exception describing
-                           the reason of invalidity.
+            :class:`~.Block`: If valid, return a `Block` object. Else an
+            appropriate exception describing the reason of invalidity is
+            raised.
 
         Raises:
-            OperationError: if a non-federation node signed the block.
+            OperationError: If a non-federation node signed the Block.
+            InvalidSignature: If a Block's signature is invalid.
         """
 
         # First, make sure this node hasn't already voted on this block
@@ -184,6 +209,15 @@ class Block(object):
         return self
 
     def sign(self, signing_key):
+        """Create a signature for the Block and overwrite `self.signature`.
+
+        Args:
+            signing_key (str): A signing key corresponding to
+                `self.node_pubkey`.
+
+        Returns:
+            :class:`~.Block`
+        """
         block_body = self.to_dict()
         block_serialized = serialize(block_body['block'])
         signing_key = SigningKey(signing_key)
@@ -191,8 +225,13 @@ class Block(object):
         return self
 
     def is_signature_valid(self):
+        """Check the validity of a Block's signature.
+
+        Returns:
+            bool: Stating the validity of the Block's signature.
+        """
         block = self.to_dict()['block']
-        # cc only accepts bytesting messages 
+        # cc only accepts bytestring messages
         block_serialized = serialize(block).encode()
         verifying_key = VerifyingKey(block['node_pubkey'])
         try:
@@ -204,6 +243,21 @@ class Block(object):
 
     @classmethod
     def from_dict(cls, block_body):
+        """Transform a Python dictionary to a Block object.
+
+        Args:
+            block_body (dict): A block dictionary to be transformed.
+
+        Returns:
+            :class:`~Block`
+
+        Raises:
+            InvalidHash: If the block's id is not corresponding to its
+                data.
+            InvalidSignature: If the block's signature is not corresponding
+                to it's data or `node_pubkey`.
+        """
+        # TODO: Reuse `is_signature_valid` method here.
         block = block_body['block']
         block_serialized = serialize(block)
         block_id = hash_data(block_serialized)
@@ -222,7 +276,7 @@ class Block(object):
             #       https://github.com/bigchaindb/cryptoconditions/issues/27
             try:
                 signature_valid = verifying_key\
-                        .verify(block_serialized.encode(), signature)
+                    .verify(block_serialized.encode(), signature)
             except ValueError:
                 signature_valid = False
             if signature_valid is False:
@@ -239,6 +293,14 @@ class Block(object):
         return self.to_dict()['id']
 
     def to_dict(self):
+        """Transform the Block to a Python dictionary.
+
+        Returns:
+            dict: The Block as a dict.
+
+        Raises:
+            OperationError: If the Block doesn't contain any transactions.
+        """
         if len(self.transactions) == 0:
             raise OperationError('Empty block creation is not allowed')
 
diff --git a/bigchaindb/pipelines/block.py b/bigchaindb/pipelines/block.py
index 0d5e24b2..4142b234 100644
--- a/bigchaindb/pipelines/block.py
+++ b/bigchaindb/pipelines/block.py
@@ -69,10 +69,7 @@ class BlockPipeline:
                 # if the tx is already in a valid or undecided block,
                 # then it no longer should be in the backlog, or added
                 # to a new block. We can delete and drop it.
-                self.bigchain.connection.run(
-                    r.table('backlog')
-                    .get(tx.id)
-                    .delete(durability='hard'))
+                self.bigchain.delete_transaction(tx.id)
                 return None
 
         tx_validated = self.bigchain.is_valid_transaction(tx)
@@ -81,10 +78,7 @@ class BlockPipeline:
         else:
             # if the transaction is not valid, remove it from the
             # backlog
-            self.bigchain.connection.run(
-                r.table('backlog')
-                .get(tx.id)
-                .delete(durability='hard'))
+            self.bigchain.delete_transaction(tx.id)
             return None
 
     def create(self, tx, timeout=False):
@@ -136,10 +130,7 @@ class BlockPipeline:
         Returns:
             :class:`~bigchaindb.models.Block`: The block.
         """
-        self.bigchain.connection.run(
-            r.table('backlog')
-            .get_all(*[tx.id for tx in block.transactions])
-            .delete(durability='hard'))
+        self.bigchain.delete_transaction(*[tx.id for tx in block.transactions])
         return block
 
 
diff --git a/bigchaindb/pipelines/utils.py b/bigchaindb/pipelines/utils.py
index 26984500..71f740ee 100644
--- a/bigchaindb/pipelines/utils.py
+++ b/bigchaindb/pipelines/utils.py
@@ -73,4 +73,3 @@ class ChangeFeed(Node):
                 self.outqueue.put(change['old_val'])
             elif is_update and (self.operation & ChangeFeed.UPDATE):
                 self.outqueue.put(change['new_val'])
-
diff --git a/bigchaindb/pipelines/vote.py b/bigchaindb/pipelines/vote.py
index 6b12f55b..b89e0786 100644
--- a/bigchaindb/pipelines/vote.py
+++ b/bigchaindb/pipelines/vote.py
@@ -40,10 +40,11 @@ class Vote:
         self.validity = {}
 
         self.invalid_dummy_tx = Transaction.create([self.bigchain.me],
-                                                   [self.bigchain.me])
+                                                   [([self.bigchain.me], 1)])
 
     def validate_block(self, block):
-        if not self.bigchain.has_previous_vote(block['id'], block['block']['voters']):
+        if not self.bigchain.has_previous_vote(block['id'],
+                                               block['block']['voters']):
             try:
                 block = Block.from_dict(block)
             except (exceptions.InvalidHash, exceptions.InvalidSignature):
diff --git a/bigchaindb/web/views/base.py b/bigchaindb/web/views/base.py
index 82fdc418..9282b5b9 100644
--- a/bigchaindb/web/views/base.py
+++ b/bigchaindb/web/views/base.py
@@ -12,4 +12,3 @@ def make_error(status_code, message=None):
     })
     response.status_code = status_code
     return response
-
diff --git a/deploy-cluster-aws/example_deploy_conf.py b/deploy-cluster-aws/example_deploy_conf.py
index a36cd6e6..5d22e52b 100644
--- a/deploy-cluster-aws/example_deploy_conf.py
+++ b/deploy-cluster-aws/example_deploy_conf.py
@@ -44,9 +44,8 @@ USE_KEYPAIRS_FILE=False
 # and you can search for one that meets your needs at:
 # https://cloud-images.ubuntu.com/locator/ec2/
 # Example:
-# "ami-72c33e1d"
-# (eu-central-1 Ubuntu 14.04 LTS amd64 hvm:ebs-ssd 20160919)
-IMAGE_ID="ami-72c33e1d"
+# (eu-central-1 Ubuntu 14.04 LTS amd64 hvm:ebs-ssd 20161020)
+IMAGE_ID="ami-9c09f0f3"
 
 # INSTANCE_TYPE is the type of AWS instance to launch
 # i.e. How many CPUs do you want? How much storage? etc.
diff --git a/docs/root/source/data-models/transaction-model.md b/docs/root/source/data-models/transaction-model.md
index 881ab8b4..f8cb5929 100644
--- a/docs/root/source/data-models/transaction-model.md
+++ b/docs/root/source/data-models/transaction-model.md
@@ -28,11 +28,11 @@ Here's some explanation of the contents of a transaction:
     - `fulfillments`: List of fulfillments. Each _fulfillment_ contains a pointer to an unspent asset
     and a _crypto fulfillment_ that satisfies a spending condition set on the unspent asset. A _fulfillment_
     is usually a signature proving the ownership of the asset.
-    See [Conditions and Fulfillments](#conditions-and-fulfillments) below.
+    See the page about [Crypto-Conditions and Fulfillments](crypto-conditions.html).
     - `conditions`: List of conditions. Each _condition_ is a _crypto-condition_ that needs to be fulfilled by a transfer transaction in order to transfer ownership to new owners.
-    See [Conditions and Fulfillments](#conditions-and-fulfillments) below.
+    See the page about [Crypto-Conditions and Fulfillments](crypto-conditions.html).
     - `operation`: String representation of the operation being performed (currently either "CREATE", "TRANSFER" or "GENESIS"). It determines how the transaction should be validated.
-    - `timestamp`: The Unix time when the transaction was created. It's provided by the client. See [the section on timestamps](timestamps.html).
+    - `timestamp`: The Unix time when the transaction was created. It's provided by the client. See the page about [timestamps in BigchainDB](../timestamps.html).
 	- `asset`: Definition of the digital asset. See next section.
     - `metadata`:
         - `id`: UUID version 4 (random) converted to a string of hex digits in standard form.
diff --git a/docs/root/source/transaction-concepts.md b/docs/root/source/transaction-concepts.md
index 718915ec..541cd886 100644
--- a/docs/root/source/transaction-concepts.md
+++ b/docs/root/source/transaction-concepts.md
@@ -12,11 +12,18 @@ A creation transaction also establishes the conditions that must be met to trans
 
 A _transfer transaction_ can transfer an asset by fulfilling the current conditions on the asset. It can also specify new transfer conditions.
 
-Today, every transaction contains one fulfillment-condition pair. The fulfillment in a transfer transaction must correspond to a condition in a previous transaction.
+Today, every transaction contains one fulfillment-condition pair. The fulfillment in a transfer transaction must fulfill a condition in a previous transaction.
 
-When a node is asked to check the validity of a transaction, it must do several things, including:
+When a node is asked to check if a transaction is valid, it checks several things. Some things it checks are:
 
-* double-spending checks (for transfer transactions),
-* hash validation (i.e. is the calculated transaction hash equal to its id?), and
-* validation of all fulfillments, including validation of cryptographic signatures if they’re among the conditions.
+* Are all the fulfillments valid? (Do they correctly satisfy the conditions they claim to satisfy?)
+* If it's a creation transaction, is the asset valid?
+* If it's a transfer transaction:
+   * Is it trying to fulfill a condition in a nonexistent transaction?
+   * Is it trying to fulfill a condition that's not in a valid transaction? (It's okay if the condition is in a transaction in an invalid block; those transactions are ignored. Transactions in the backlog or undecided blocks are not ignored.)
+   * Is it trying to fulfill a condition that has already been fulfilled, or that some other pending transaction (in the backlog or an undecided block) also aims to fulfill?
+   * Is the asset ID in the transaction the same as the asset ID in all transactions whose conditions are being fulfilled?
 
+If you're curious about the details of transaction validation, the code is in the `validate` method of the `Transaction` class, in `bigchaindb/models.py` (at the time of writing).
+
+Note: The check to see if the transaction ID is equal to the hash of the transaction body is actually done whenever the transaction is converted from a Python dict to a Transaction object, which must be done before the `validate` method can be called (since it's called on a Transaction object).
diff --git a/docs/server/source/clusters-feds/aws-testing-cluster.md b/docs/server/source/clusters-feds/aws-testing-cluster.md
index 61557102..e829fcbb 100644
--- a/docs/server/source/clusters-feds/aws-testing-cluster.md
+++ b/docs/server/source/clusters-feds/aws-testing-cluster.md
@@ -126,7 +126,7 @@ BRANCH="master"
 WHAT_TO_DEPLOY="servers"
 SSH_KEY_NAME="not-set-yet"
 USE_KEYPAIRS_FILE=False
-IMAGE_ID="ami-72c33e1d"
+IMAGE_ID="ami-9c09f0f3"
 INSTANCE_TYPE="t2.medium"
 SECURITY_GROUP="bigchaindb"
 USING_EBS=True
diff --git a/docs/server/source/conf.py b/docs/server/source/conf.py
index 640e3273..ab9531fd 100644
--- a/docs/server/source/conf.py
+++ b/docs/server/source/conf.py
@@ -41,7 +41,7 @@ extensions = [
     'sphinx.ext.intersphinx',
     'sphinx.ext.coverage',
     'sphinx.ext.viewcode',
-    'sphinxcontrib.napoleon',
+    'sphinx.ext.napoleon',
     'sphinxcontrib.httpdomain',
 ]
 
diff --git a/docs/server/source/drivers-clients/http-client-server-api.rst b/docs/server/source/drivers-clients/http-client-server-api.rst
index 74bcf1d2..d274efad 100644
--- a/docs/server/source/drivers-clients/http-client-server-api.rst
+++ b/docs/server/source/drivers-clients/http-client-server-api.rst
@@ -3,21 +3,35 @@ The HTTP Client-Server API
 
 .. note::
 
-   The HTTP client-server API is currently quite rudimentary. For example, there is no ability to do complex queries using the HTTP API. We plan to add querying capabilities in the future.
+   The HTTP client-server API is currently quite rudimentary. For example,
+   there is no ability to do complex queries using the HTTP API. We plan to add
+   querying capabilities in the future.
 
-When you start Bigchaindb using `bigchaindb start`, an HTTP API is exposed at the address stored in the BigchainDB node configuration settings. The default is:
+When you start Bigchaindb using `bigchaindb start`, an HTTP API is exposed at
+the address stored in the BigchainDB node configuration settings. The default
+is:
 
 `http://localhost:9984/api/v1/ <http://localhost:9984/api/v1/>`_
 
-but that address can be changed by changing the "API endpoint" configuration setting (e.g. in a local config file). There's more information about setting the API endpoint in :doc:`the section about BigchainDB Configuration Settings <../server-reference/configuration>`.
+but that address can be changed by changing the "API endpoint" configuration
+setting (e.g. in a local config file). There's more information about setting
+the API endpoint in :doc:`the section about BigchainDB Configuration Settings
+<../server-reference/configuration>`.
 
-There are other configuration settings related to the web server (serving the HTTP API). In particular, the default is for the web server socket to bind to ``localhost:9984`` but that can be changed (e.g. to ``0.0.0.0:9984``). For more details, see the "server" settings ("bind", "workers" and "threads") in :doc:`the section about BigchainDB Configuration Settings <../server-reference/configuration>`.
+There are other configuration settings related to the web server (serving the
+HTTP API). In particular, the default is for the web server socket to bind to
+``localhost:9984`` but that can be changed (e.g. to ``0.0.0.0:9984``). For more
+details, see the "server" settings ("bind", "workers" and "threads") in
+:doc:`the section about BigchainDB Configuration Settings
+<../server-reference/configuration>`.
 
 
 API Root
 --------
 
-If you send an HTTP GET request to e.g. ``http://localhost:9984`` (with no ``/api/v1/`` on the end), then you should get an HTTP response with something like the following in the body:
+If you send an HTTP GET request to e.g. ``http://localhost:9984`` (with no
+``/api/v1/`` on the end), then you should get an HTTP response with something
+like the following in the body:
 
 .. code-block:: json
 
@@ -39,8 +53,13 @@ POST /transactions/
 .. http:post:: /transactions/
 
    Push a new transaction.
-   
-   Note: The posted transaction should be valid `transaction <https://bigchaindb.readthedocs.io/en/latest/data-models/transaction-model.html>`_. The steps to build a valid transaction are beyond the scope of this page. One would normally use a driver such as the `BigchainDB Python Driver <https://docs.bigchaindb.com/projects/py-driver/en/latest/index.html>`_ to build a valid transaction.
+
+   Note: The posted transaction should be valid `transaction
+   <https://bigchaindb.readthedocs.io/en/latest/data-models/transaction-model.html>`_.
+   The steps to build a valid transaction are beyond the scope of this page.
+   One would normally use a driver such as the `BigchainDB Python Driver
+   <https://docs.bigchaindb.com/projects/py-driver/en/latest/index.html>`_ to
+   build a valid transaction.
 
    **Example request**:
 
@@ -158,9 +177,11 @@ GET /transactions/{tx_id}/status
 
 .. http:get:: /transactions/{tx_id}/status
 
-   Get the status of the transaction with the ID ``tx_id``, if a transaction with that ``tx_id`` exists.
+   Get the status of the transaction with the ID ``tx_id``, if a transaction
+   with that ``tx_id`` exists.
 
-   The possible status values are ``backlog``, ``undecided``, ``valid`` or ``invalid``.
+   The possible status values are ``backlog``, ``undecided``, ``valid`` or
+   ``invalid``.
 
    :param tx_id: transaction ID
    :type tx_id: hex string
@@ -194,7 +215,8 @@ GET /transactions/{tx_id}
 
    Get the transaction with the ID ``tx_id``.
 
-   This endpoint returns only a transaction from a ``VALID`` or ``UNDECIDED`` block on ``bigchain``, if exists.
+   This endpoint returns only a transaction from a ``VALID`` or ``UNDECIDED``
+   block on ``bigchain``, if exists.
 
    :param tx_id: transaction ID
    :type tx_id: hex string
@@ -260,4 +282,4 @@ GET /transactions/{tx_id}
       }
 
    :statuscode 200: A transaction with that ID was found.
-   :statuscode 404: A transaction with that ID was not found.
\ No newline at end of file
+   :statuscode 404: A transaction with that ID was not found.
diff --git a/setup.py b/setup.py
index 67a367f6..0f558dd7 100644
--- a/setup.py
+++ b/setup.py
@@ -31,10 +31,10 @@ check_setuptools_features()
 tests_require = [
     'coverage',
     'pep8',
-    'pyflakes',
+    'flake8',
     'pylint',
     'pytest',
-    'pytest-cov==2.2.1',
+    'pytest-cov>=2.2.1',
     'pytest-xdist',
     'pytest-flask',
 ]
@@ -48,7 +48,6 @@ docs_require = [
     'Sphinx>=1.3.5',
     'recommonmark>=0.4.0',
     'sphinx-rtd-theme>=0.1.9',
-    'sphinxcontrib-napoleon>=0.4.4',
     'sphinxcontrib-httpdomain>=1.5.0',
 ]
 
@@ -56,6 +55,20 @@ benchmarks_require = [
     'line-profiler==1.0',
 ]
 
+install_requires = [
+    'rethinkdb~=2.3',  # i.e. a version between 2.3 and 3.0
+    'pysha3>=0.3',
+    'cryptoconditions>=0.5.0',
+    'statsd>=3.2.1',
+    'python-rapidjson>=0.0.6',
+    'logstats>=0.2.1',
+    'flask>=0.10.1',
+    'flask-restful~=0.3.0',
+    'requests~=2.9',
+    'gunicorn~=19.0',
+    'multipipes~=0.1.0',
+]
+
 setup(
     name='BigchainDB',
     version=version['__version__'],
@@ -75,7 +88,7 @@ setup(
         'Topic :: Software Development',
         'Natural Language :: English',
         'License :: OSI Approved :: GNU Affero General Public License v3',
-        'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3 :: Only',
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Operating System :: MacOS :: MacOS X',
@@ -89,21 +102,7 @@ setup(
             'bigchaindb=bigchaindb.commands.bigchain:main'
         ],
     },
-    install_requires=[
-        'rethinkdb~=2.3',
-        'pysha3==0.3',
-        'pytz==2015.7',
-        'cryptoconditions==0.5.0',
-        'statsd==3.2.1',
-        'python-rapidjson==0.0.6',
-        'logstats==0.2.1',
-        'base58==0.2.2',
-        'flask==0.10.1',
-        'flask-restful~=0.3.0',
-        'requests~=2.9',
-        'gunicorn~=19.0',
-        'multipipes~=0.1.0',
-    ],
+    install_requires=install_requires,
     setup_requires=['pytest-runner'],
     tests_require=tests_require,
     extras_require={
diff --git a/tests/assets/test_digital_assets.py b/tests/assets/test_digital_assets.py
index e18684c5..56a08d53 100644
--- a/tests/assets/test_digital_assets.py
+++ b/tests/assets/test_digital_assets.py
@@ -1,5 +1,7 @@
 import pytest
-from ..db.conftest import inputs
+from unittest.mock import patch
+
+from ..db.conftest import inputs  # noqa
 
 
 @pytest.mark.usefixtures('inputs')
@@ -9,7 +11,7 @@ def test_asset_transfer(b, user_vk, user_sk):
     tx_input = b.get_owned_ids(user_vk).pop()
     tx_create = b.get_transaction(tx_input.txid)
 
-    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [user_vk],
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([user_vk], 1)],
                                        tx_create.asset)
     tx_transfer_signed = tx_transfer.sign([user_sk])
 
@@ -18,61 +20,40 @@ def test_asset_transfer(b, user_vk, user_sk):
 
 
 def test_validate_bad_asset_creation(b, user_vk):
-    from bigchaindb.models import Transaction
+    from bigchaindb.models import Transaction, Asset
 
     # `divisible` needs to be a boolean
-    tx = Transaction.create([b.me], [user_vk])
+    tx = Transaction.create([b.me], [([user_vk], 1)])
     tx.asset.divisible = 1
-    tx_signed = tx.sign([b.me_private])
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx_signed = tx.sign([b.me_private])
     with pytest.raises(TypeError):
         tx_signed.validate(b)
 
     # `refillable` needs to be a boolean
-    tx = Transaction.create([b.me], [user_vk])
+    tx = Transaction.create([b.me], [([user_vk], 1)])
     tx.asset.refillable = 1
-    tx_signed = tx.sign([b.me_private])
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx_signed = tx.sign([b.me_private])
     with pytest.raises(TypeError):
         b.validate_transaction(tx_signed)
 
     # `updatable` needs to be a boolean
-    tx = Transaction.create([b.me], [user_vk])
+    tx = Transaction.create([b.me], [([user_vk], 1)])
     tx.asset.updatable = 1
-    tx_signed = tx.sign([b.me_private])
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx_signed = tx.sign([b.me_private])
     with pytest.raises(TypeError):
         b.validate_transaction(tx_signed)
 
     # `data` needs to be a dictionary
-    tx = Transaction.create([b.me], [user_vk])
+    tx = Transaction.create([b.me], [([user_vk], 1)])
     tx.asset.data = 'a'
-    tx_signed = tx.sign([b.me_private])
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx_signed = tx.sign([b.me_private])
     with pytest.raises(TypeError):
         b.validate_transaction(tx_signed)
 
-    # TODO: Check where to test for the amount
-    """
-    tx = b.create_transaction(b.me, user_vk, None, 'CREATE')
-    tx['transaction']['conditions'][0]['amount'] = 'a'
-    tx['id'] = get_hash_data(tx['transaction'])
-    tx_signed = b.sign_transaction(tx, b.me_private)
-    with pytest.raises(TypeError):
-        b.validate_transaction(tx_signed)
-
-    tx = b.create_transaction(b.me, user_vk, None, 'CREATE')
-    tx['transaction']['conditions'][0]['amount'] = 2
-    tx['transaction']['asset'].update({'divisible': False})
-    tx['id'] = get_hash_data(tx['transaction'])
-    tx_signed = b.sign_transaction(tx, b.me_private)
-    with pytest.raises(AmountError):
-        b.validate_transaction(tx_signed)
-
-    tx = b.create_transaction(b.me, user_vk, None, 'CREATE')
-    tx['transaction']['conditions'][0]['amount'] = 0
-    tx['id'] = get_hash_data(tx['transaction'])
-    tx_signed = b.sign_transaction(tx, b.me_private)
-    with pytest.raises(AmountError):
-        b.validate_transaction(tx_signed)
-    """
-
 
 @pytest.mark.usefixtures('inputs')
 def test_validate_transfer_asset_id_mismatch(b, user_vk, user_sk):
@@ -81,7 +62,7 @@ def test_validate_transfer_asset_id_mismatch(b, user_vk, user_sk):
 
     tx_create = b.get_owned_ids(user_vk).pop()
     tx_create = b.get_transaction(tx_create.txid)
-    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [user_vk],
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([user_vk], 1)],
                                        tx_create.asset)
     tx_transfer.asset.data_id = 'aaa'
     tx_transfer_signed = tx_transfer.sign([user_sk])
@@ -92,7 +73,7 @@ def test_validate_transfer_asset_id_mismatch(b, user_vk, user_sk):
 def test_get_asset_id_create_transaction(b, user_vk):
     from bigchaindb.models import Transaction, Asset
 
-    tx_create = Transaction.create([b.me], [user_vk])
+    tx_create = Transaction.create([b.me], [([user_vk], 1)])
     asset_id = Asset.get_asset_id(tx_create)
 
     assert asset_id == tx_create.asset.data_id
@@ -105,7 +86,7 @@ def test_get_asset_id_transfer_transaction(b, user_vk, user_sk):
     tx_create = b.get_owned_ids(user_vk).pop()
     tx_create = b.get_transaction(tx_create.txid)
     # create a transfer transaction
-    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [user_vk],
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([user_vk], 1)],
                                        tx_create.asset)
     tx_transfer_signed = tx_transfer.sign([user_sk])
     # create a block
@@ -123,8 +104,8 @@ def test_asset_id_mismatch(b, user_vk):
     from bigchaindb.models import Transaction, Asset
     from bigchaindb.common.exceptions import AssetIdMismatch
 
-    tx1 = Transaction.create([b.me], [user_vk])
-    tx2 = Transaction.create([b.me], [user_vk])
+    tx1 = Transaction.create([b.me], [([user_vk], 1)])
+    tx2 = Transaction.create([b.me], [([user_vk], 1)])
 
     with pytest.raises(AssetIdMismatch):
         Asset.get_asset_id([tx1, tx2])
@@ -144,7 +125,7 @@ def test_get_txs_by_asset_id(b, user_vk, user_sk):
     assert txs[0].asset.data_id == asset_id
 
     # create a transfer transaction
-    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [user_vk],
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([user_vk], 1)],
                                        tx_create.asset)
     tx_transfer_signed = tx_transfer.sign([user_sk])
     # create the block
@@ -161,3 +142,73 @@ def test_get_txs_by_asset_id(b, user_vk, user_sk):
     assert tx_transfer.id in [t.id for t in txs]
     assert asset_id == txs[0].asset.data_id
     assert asset_id == txs[1].asset.data_id
+
+
+@pytest.mark.usefixtures('inputs')
+def test_get_asset_by_id(b, user_vk, user_sk):
+    from bigchaindb.models import Transaction
+
+    tx_create = b.get_owned_ids(user_vk).pop()
+    tx_create = b.get_transaction(tx_create.txid)
+    asset_id = tx_create.asset.data_id
+
+    # create a transfer transaction
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([user_vk], 1)],
+                                       tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+    # create the block
+    block = b.create_block([tx_transfer_signed])
+    b.write_block(block, durability='hard')
+    # vote the block valid
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    txs = b.get_txs_by_asset_id(asset_id)
+    assert len(txs) == 2
+
+    asset = b.get_asset_by_id(asset_id)
+    assert asset == tx_create.asset
+
+
+def test_create_invalid_divisible_asset(b, user_vk, user_sk):
+    from bigchaindb.models import Transaction, Asset
+    from bigchaindb.common.exceptions import AmountError
+
+    # non divisible assets cannot have amount > 1
+    # Transaction.__init__ should raise an exception
+    asset = Asset(divisible=False)
+    with pytest.raises(AmountError):
+        Transaction.create([user_vk], [([user_vk], 2)], asset=asset)
+
+    # divisible assets need to have an amount > 1
+    # Transaction.__init__ should raise an exception
+    asset = Asset(divisible=True)
+    with pytest.raises(AmountError):
+        Transaction.create([user_vk], [([user_vk], 1)], asset=asset)
+
+    # even if a transaction is badly constructed the server should raise the
+    # exception
+    asset = Asset(divisible=False)
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction.create([user_vk], [([user_vk], 2)], asset=asset)
+        tx_signed = tx.sign([user_sk])
+    with pytest.raises(AmountError):
+        tx_signed.validate(b)
+    assert b.is_valid_transaction(tx_signed) is False
+
+    asset = Asset(divisible=True)
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction.create([user_vk], [([user_vk], 1)], asset=asset)
+        tx_signed = tx.sign([user_sk])
+    with pytest.raises(AmountError):
+        tx_signed.validate(b)
+    assert b.is_valid_transaction(tx_signed) is False
+
+
+def test_create_valid_divisible_asset(b, user_vk, user_sk):
+    from bigchaindb.models import Transaction, Asset
+
+    asset = Asset(divisible=True)
+    tx = Transaction.create([user_vk], [([user_vk], 2)], asset=asset)
+    tx_signed = tx.sign([user_sk])
+    assert b.is_valid_transaction(tx_signed)
diff --git a/tests/assets/test_divisible_assets.py b/tests/assets/test_divisible_assets.py
new file mode 100644
index 00000000..5ae360e0
--- /dev/null
+++ b/tests/assets/test_divisible_assets.py
@@ -0,0 +1,779 @@
+import pytest
+
+from unittest.mock import patch
+
+from ..db.conftest import inputs  # noqa
+
+
+# CREATE divisible asset
+# Single input
+# Single owners_before
+# Single output
+# Single owners_after
+def test_single_in_single_own_single_out_single_own_create(b, user_vk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    asset = Asset(divisible=True)
+    tx = Transaction.create([b.me], [([user_vk], 100)], asset=asset)
+    tx_signed = tx.sign([b.me_private])
+
+    assert tx_signed.validate(b) == tx_signed
+    assert len(tx_signed.conditions) == 1
+    assert tx_signed.conditions[0].amount == 100
+    assert len(tx_signed.fulfillments) == 1
+
+
+# CREATE divisible asset
+# Single input
+# Single owners_before
+# Multiple outputs
+# Single owners_after per output
+def test_single_in_single_own_multiple_out_single_own_create(b, user_vk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    asset = Asset(divisible=True)
+    tx = Transaction.create([b.me], [([user_vk], 50), ([user_vk], 50)],
+                            asset=asset)
+    tx_signed = tx.sign([b.me_private])
+
+    assert tx_signed.validate(b) == tx_signed
+    assert len(tx_signed.conditions) == 2
+    assert tx_signed.conditions[0].amount == 50
+    assert tx_signed.conditions[1].amount == 50
+    assert len(tx_signed.fulfillments) == 1
+
+
+# CREATE divisible asset
+# Single input
+# Single owners_before
+# Single output
+# Multiple owners_after
+def test_single_in_single_own_single_out_multiple_own_create(b, user_vk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    asset = Asset(divisible=True)
+    tx = Transaction.create([b.me], [([user_vk, user_vk], 100)], asset=asset)
+    tx_signed = tx.sign([b.me_private])
+
+    assert tx_signed.validate(b) == tx_signed
+    assert len(tx_signed.conditions) == 1
+    assert tx_signed.conditions[0].amount == 100
+
+    condition = tx_signed.conditions[0].to_dict()
+    assert 'subfulfillments' in condition['condition']['details']
+    assert len(condition['condition']['details']['subfulfillments']) == 2
+
+    assert len(tx_signed.fulfillments) == 1
+
+
+# CREATE divisible asset
+# Single input
+# Single owners_before
+# Multiple outputs
+# Mix: one output with a single owners_after, one output with multiple
+#      owners_after
+def test_single_in_single_own_multiple_out_mix_own_create(b, user_vk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    asset = Asset(divisible=True)
+    tx = Transaction.create([b.me],
+                            [([user_vk], 50), ([user_vk, user_vk], 50)],
+                            asset=asset)
+    tx_signed = tx.sign([b.me_private])
+
+    assert tx_signed.validate(b) == tx_signed
+    assert len(tx_signed.conditions) == 2
+    assert tx_signed.conditions[0].amount == 50
+    assert tx_signed.conditions[1].amount == 50
+
+    condition_cid1 = tx_signed.conditions[1].to_dict()
+    assert 'subfulfillments' in condition_cid1['condition']['details']
+    assert len(condition_cid1['condition']['details']['subfulfillments']) == 2
+
+    assert len(tx_signed.fulfillments) == 1
+
+
+# CREATE divisible asset
+# Single input
+# Multiple owners_before
+# Output combinations already tested above
+def test_single_in_multiple_own_single_out_single_own_create(b, user_vk,
+                                                             user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    asset = Asset(divisible=True)
+    tx = Transaction.create([b.me, user_vk], [([user_vk], 100)], asset=asset)
+    tx_signed = tx.sign([b.me_private, user_sk])
+    assert tx_signed.validate(b) == tx_signed
+    assert len(tx_signed.conditions) == 1
+    assert tx_signed.conditions[0].amount == 100
+    assert len(tx_signed.fulfillments) == 1
+
+    ffill = tx_signed.fulfillments[0].fulfillment.to_dict()
+    assert 'subfulfillments' in ffill
+    assert len(ffill['subfulfillments']) == 2
+
+
+# TRANSFER divisible asset
+# Single input
+# Single owners_before
+# Single output
+# Single owners_after
+# TODO: I don't really need inputs. But I need the database to be setup or
+#       else there will be no genesis block and b.get_last_voted_block will
+#       fail.
+#       Is there a better way of doing this?
+@pytest.mark.usefixtures('inputs')
+def test_single_in_single_own_single_out_single_own_transfer(b, user_vk,
+                                                             user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 100)], asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 100)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+
+    assert tx_transfer_signed.validate(b)
+    assert len(tx_transfer_signed.conditions) == 1
+    assert tx_transfer_signed.conditions[0].amount == 100
+    assert len(tx_transfer_signed.fulfillments) == 1
+
+
+# TRANSFER divisible asset
+# Single input
+# Single owners_before
+# Multiple output
+# Single owners_after
+@pytest.mark.usefixtures('inputs')
+def test_single_in_single_own_multiple_out_single_own_transfer(b, user_vk,
+                                                               user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 100)], asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(),
+                                       [([b.me], 50), ([b.me], 50)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+    assert len(tx_transfer_signed.conditions) == 2
+    assert tx_transfer_signed.conditions[0].amount == 50
+    assert tx_transfer_signed.conditions[1].amount == 50
+    assert len(tx_transfer_signed.fulfillments) == 1
+
+
+# TRANSFER divisible asset
+# Single input
+# Single owners_before
+# Single output
+# Multiple owners_after
+@pytest.mark.usefixtures('inputs')
+def test_single_in_single_own_single_out_multiple_own_transfer(b, user_vk,
+                                                               user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 100)], asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(),
+                                       [([b.me, b.me], 100)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+    assert len(tx_transfer_signed.conditions) == 1
+    assert tx_transfer_signed.conditions[0].amount == 100
+
+    condition = tx_transfer_signed.conditions[0].to_dict()
+    assert 'subfulfillments' in condition['condition']['details']
+    assert len(condition['condition']['details']['subfulfillments']) == 2
+
+    assert len(tx_transfer_signed.fulfillments) == 1
+
+
+# TRANSFER divisible asset
+# Single input
+# Single owners_before
+# Multiple outputs
+# Mix: one output with a single owners_after, one output with multiple
+#      owners_after
+@pytest.mark.usefixtures('inputs')
+def test_single_in_single_own_multiple_out_mix_own_transfer(b, user_vk,
+                                                            user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 100)], asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(),
+                                       [([b.me], 50), ([b.me, b.me], 50)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+    assert len(tx_transfer_signed.conditions) == 2
+    assert tx_transfer_signed.conditions[0].amount == 50
+    assert tx_transfer_signed.conditions[1].amount == 50
+
+    condition_cid1 = tx_transfer_signed.conditions[1].to_dict()
+    assert 'subfulfillments' in condition_cid1['condition']['details']
+    assert len(condition_cid1['condition']['details']['subfulfillments']) == 2
+
+    assert len(tx_transfer_signed.fulfillments) == 1
+
+
+# TRANSFER divisible asset
+# Single input
+# Multiple owners_before
+# Single output
+# Single owners_after
+@pytest.mark.usefixtures('inputs')
+def test_single_in_multiple_own_single_out_single_own_transfer(b, user_vk,
+                                                               user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([b.me, user_vk], 100)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 100)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([b.me_private, user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+    assert len(tx_transfer_signed.conditions) == 1
+    assert tx_transfer_signed.conditions[0].amount == 100
+    assert len(tx_transfer_signed.fulfillments) == 1
+
+    ffill = tx_transfer_signed.fulfillments[0].fulfillment.to_dict()
+    assert 'subfulfillments' in ffill
+    assert len(ffill['subfulfillments']) == 2
+
+
+# TRANSFER divisible asset
+# Multiple inputs
+# Single owners_before per input
+# Single output
+# Single owners_after
+@pytest.mark.usefixtures('inputs')
+def test_multiple_in_single_own_single_out_single_own_transfer(b, user_vk,
+                                                               user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 50), ([user_vk], 50)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 100)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+
+    assert tx_transfer_signed.validate(b)
+    assert len(tx_transfer_signed.conditions) == 1
+    assert tx_transfer_signed.conditions[0].amount == 100
+    assert len(tx_transfer_signed.fulfillments) == 2
+
+
+# TRANSFER divisible asset
+# Multiple inputs
+# Multiple owners_before per input
+# Single output
+# Single owners_after
+@pytest.mark.usefixtures('inputs')
+def test_multiple_in_multiple_own_single_out_single_own_transfer(b, user_vk,
+                                                                 user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me],
+                                   [([user_vk, b.me], 50),
+                                    ([user_vk, b.me], 50)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 100)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([b.me_private, user_sk])
+
+    assert tx_transfer_signed.validate(b)
+    assert len(tx_transfer_signed.conditions) == 1
+    assert tx_transfer_signed.conditions[0].amount == 100
+    assert len(tx_transfer_signed.fulfillments) == 2
+
+    ffill_fid0 = tx_transfer_signed.fulfillments[0].fulfillment.to_dict()
+    ffill_fid1 = tx_transfer_signed.fulfillments[1].fulfillment.to_dict()
+    assert 'subfulfillments' in ffill_fid0
+    assert 'subfulfillments' in ffill_fid1
+    assert len(ffill_fid0['subfulfillments']) == 2
+    assert len(ffill_fid1['subfulfillments']) == 2
+
+
+# TRANSFER divisible asset
+# Multiple inputs
+# Mix: one input with a single owners_before, one input with multiple
+#      owners_before
+# Single output
+# Single owners_after
+@pytest.mark.usefixtures('inputs')
+def test_muiltiple_in_mix_own_multiple_out_single_own_transfer(b, user_vk,
+                                                               user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me],
+                                   [([user_vk], 50),
+                                    ([user_vk, b.me], 50)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 100)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([b.me_private, user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+    assert len(tx_transfer_signed.conditions) == 1
+    assert tx_transfer_signed.conditions[0].amount == 100
+    assert len(tx_transfer_signed.fulfillments) == 2
+
+    ffill_fid0 = tx_transfer_signed.fulfillments[0].fulfillment.to_dict()
+    ffill_fid1 = tx_transfer_signed.fulfillments[1].fulfillment.to_dict()
+    assert 'subfulfillments' not in ffill_fid0
+    assert 'subfulfillments' in ffill_fid1
+    assert len(ffill_fid1['subfulfillments']) == 2
+
+
+# TRANSFER divisible asset
+# Multiple inputs
+# Mix: one input with a single owners_before, one input with multiple
+#      owners_before
+# Multiple outputs
+# Mix: one output with a single owners_after, one output with multiple
+#      owners_after
+@pytest.mark.usefixtures('inputs')
+def test_muiltiple_in_mix_own_multiple_out_mix_own_transfer(b, user_vk,
+                                                            user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me],
+                                   [([user_vk], 50),
+                                    ([user_vk, b.me], 50)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(),
+                                       [([b.me], 50), ([b.me, user_vk], 50)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([b.me_private, user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+    assert len(tx_transfer_signed.conditions) == 2
+    assert tx_transfer_signed.conditions[0].amount == 50
+    assert tx_transfer_signed.conditions[1].amount == 50
+    assert len(tx_transfer_signed.fulfillments) == 2
+
+    cond_cid0 = tx_transfer_signed.conditions[0].to_dict()
+    cond_cid1 = tx_transfer_signed.conditions[1].to_dict()
+    assert 'subfulfillments' not in cond_cid0['condition']['details']
+    assert 'subfulfillments' in cond_cid1['condition']['details']
+    assert len(cond_cid1['condition']['details']['subfulfillments']) == 2
+
+    ffill_fid0 = tx_transfer_signed.fulfillments[0].fulfillment.to_dict()
+    ffill_fid1 = tx_transfer_signed.fulfillments[1].fulfillment.to_dict()
+    assert 'subfulfillments' not in ffill_fid0
+    assert 'subfulfillments' in ffill_fid1
+    assert len(ffill_fid1['subfulfillments']) == 2
+
+
+# TRANSFER divisible asset
+# Multiple inputs from different transactions
+# Single owners_before
+# Single output
+# Single owners_after
+@pytest.mark.usefixtures('inputs')
+def test_multiple_in_different_transactions(b, user_vk, user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    # `b` creates a divisible asset and assigns 50 shares to `b` and
+    # 50 shares to `user_vk`
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me],
+                                   [([user_vk], 50),
+                                    ([b.me], 50)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER divisible asset
+    # `b` transfers its 50 shares to `user_vk`
+    # after this transaction `user_vk` will have a total of 100 shares
+    # split across two different transactions
+    tx_transfer1 = Transaction.transfer(tx_create.to_inputs([1]),
+                                        [([user_vk], 50)],
+                                        asset=tx_create.asset)
+    tx_transfer1_signed = tx_transfer1.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_transfer1_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    # `user_vk` combines two different transaction with 50 shares each and
+    # transfers a total of 100 shares back to `b`
+    tx_transfer2 = Transaction.transfer(tx_create.to_inputs([0]) +
+                                        tx_transfer1.to_inputs([0]),
+                                        [([b.me], 100)],
+                                        asset=tx_create.asset)
+    tx_transfer2_signed = tx_transfer2.sign([user_sk])
+
+    assert tx_transfer2_signed.validate(b) == tx_transfer2_signed
+    assert len(tx_transfer2_signed.conditions) == 1
+    assert tx_transfer2_signed.conditions[0].amount == 100
+    assert len(tx_transfer2_signed.fulfillments) == 2
+
+    fid0_input = tx_transfer2_signed.fulfillments[0].to_dict()['input']['txid']
+    fid1_input = tx_transfer2_signed.fulfillments[1].to_dict()['input']['txid']
+    assert fid0_input == tx_create.id
+    assert fid1_input == tx_transfer1.id
+
+
+# In a TRANSFER transaction of a divisible asset the amount being spent in the
+# inputs needs to match the amount being sent in the outputs.
+# In other words `amount_in_inputs - amount_in_outputs == 0`
+@pytest.mark.usefixtures('inputs')
+def test_amount_error_transfer(b, user_vk, user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+    from bigchaindb.common.exceptions import AmountError
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 100)], asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    # output amount less than input amount
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 50)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+    with pytest.raises(AmountError):
+        tx_transfer_signed.validate(b)
+
+    # TRANSFER
+    # output amount greater than input amount
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 101)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+    with pytest.raises(AmountError):
+        tx_transfer_signed.validate(b)
+
+
+@pytest.mark.skip(reason='Figure out how to handle this case')
+@pytest.mark.usefixtures('inputs')
+def test_threshold_same_public_key(b, user_vk, user_sk):
+    # If we try to fulfill a threshold condition where each subcondition has
+    # the same key get_subcondition_from_vk will always return the first
+    # subcondition. This means that only the 1st subfulfillment will be
+    # generated
+    # Creating threshold conditions with the same key does not make sense but
+    # that does not mean that the code shouldn't work.
+
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk, user_vk], 100)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # TRANSFER
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 100)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk, user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+
+
+@pytest.mark.usefixtures('inputs')
+def test_sum_amount(b, user_vk, user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset with 3 outputs with amount 1
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me],
+                                   [([user_vk], 1),
+                                    ([user_vk], 1),
+                                    ([user_vk], 1)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # create a transfer transaction with one output and check if the amount
+    # is 3
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(), [([b.me], 3)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+    assert len(tx_transfer_signed.conditions) == 1
+    assert tx_transfer_signed.conditions[0].amount == 3
+
+
+@pytest.mark.usefixtures('inputs')
+def test_divide(b, user_vk, user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+
+    # CREATE divisible asset with 1 output with amount 3
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 3)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # create a transfer transaction with 3 outputs and check if the amount
+    # of each output is 1
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(),
+                                       [([b.me], 1), ([b.me], 1), ([b.me], 1)],
+                                       asset=tx_create.asset)
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+
+    assert tx_transfer_signed.validate(b) == tx_transfer_signed
+    assert len(tx_transfer_signed.conditions) == 3
+    for condition in tx_transfer_signed.conditions:
+        assert condition.amount == 1
+
+
+# Check that negative inputs are caught when creating a TRANSFER transaction
+@pytest.mark.usefixtures('inputs')
+def test_non_positive_amounts_on_transfer(b, user_vk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+    from bigchaindb.common.exceptions import AmountError
+
+    # CREATE divisible asset with 1 output with amount 3
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 3)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    with pytest.raises(AmountError):
+        Transaction.transfer(tx_create.to_inputs(),
+                             [([b.me], 4), ([b.me], -1)],
+                             asset=tx_create.asset)
+
+
+# Check that negative inputs are caught when validating a TRANSFER transaction
+@pytest.mark.usefixtures('inputs')
+def test_non_positive_amounts_on_transfer_validate(b, user_vk, user_sk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+    from bigchaindb.common.exceptions import AmountError
+
+    # CREATE divisible asset with 1 output with amount 3
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 3)],
+                                   asset=asset)
+    tx_create_signed = tx_create.sign([b.me_private])
+    # create block
+    block = b.create_block([tx_create_signed])
+    assert block.validate(b) == block
+    b.write_block(block, durability='hard')
+    # vote
+    vote = b.vote(block.id, b.get_last_voted_block().id, True)
+    b.write_vote(vote)
+
+    # create a transfer transaction with 3 outputs and check if the amount
+    # of each output is 1
+    tx_transfer = Transaction.transfer(tx_create.to_inputs(),
+                                       [([b.me], 4), ([b.me], 1)],
+                                       asset=tx_create.asset)
+    tx_transfer.conditions[1].amount = -1
+    tx_transfer_signed = tx_transfer.sign([user_sk])
+
+    with pytest.raises(AmountError):
+        tx_transfer_signed.validate(b)
+
+
+# Check that negative inputs are caught when creating a CREATE transaction
+@pytest.mark.usefixtures('inputs')
+def test_non_positive_amounts_on_create(b, user_vk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+    from bigchaindb.common.exceptions import AmountError
+
+    # CREATE divisible asset with 1 output with amount 3
+    asset = Asset(divisible=True)
+    with pytest.raises(AmountError):
+        Transaction.create([b.me], [([user_vk], -3)],
+                           asset=asset)
+
+
+# Check that negative inputs are caught when validating a CREATE transaction
+@pytest.mark.usefixtures('inputs')
+def test_non_positive_amounts_on_create_validate(b, user_vk):
+    from bigchaindb.models import Transaction
+    from bigchaindb.common.transaction import Asset
+    from bigchaindb.common.exceptions import AmountError
+
+    # CREATE divisible asset with 1 output with amount 3
+    asset = Asset(divisible=True)
+    tx_create = Transaction.create([b.me], [([user_vk], 3)],
+                                   asset=asset)
+    tx_create.conditions[0].amount = -3
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx_create_signed = tx_create.sign([b.me_private])
+
+    with pytest.raises(AmountError):
+        tx_create_signed.validate(b)
diff --git a/tests/common/test_asset.py b/tests/common/test_asset.py
index edfbcb5f..f6a3f89d 100644
--- a/tests/common/test_asset.py
+++ b/tests/common/test_asset.py
@@ -22,6 +22,7 @@ def test_asset_creation_with_data(data):
 def test_asset_invalid_asset_initialization():
     from bigchaindb.common.transaction import Asset
 
+    # check types
     with raises(TypeError):
         Asset(data='some wrong type')
     with raises(TypeError):
@@ -31,6 +32,12 @@ def test_asset_invalid_asset_initialization():
     with raises(TypeError):
         Asset(updatable=1)
 
+    # check for features that are not yet implemented
+    with raises(NotImplementedError):
+        Asset(updatable=True)
+    with raises(NotImplementedError):
+        Asset(refillable=True)
+
 
 def test_invalid_asset_comparison(data, data_id):
     from bigchaindb.common.transaction import Asset
@@ -69,12 +76,17 @@ def test_asset_deserialization(data, data_id):
 
 def test_validate_asset():
     from bigchaindb.common.transaction import Asset
+    from bigchaindb.common.exceptions import AmountError
 
+    # test amount errors
+    asset = Asset(divisible=False)
+    with raises(AmountError):
+        asset.validate_asset(amount=2)
+
+    asset = Asset(divisible=True)
+    with raises(AmountError):
+        asset.validate_asset(amount=1)
+
+    asset = Asset()
     with raises(TypeError):
-        Asset(divisible=1)
-    with raises(TypeError):
-        Asset(refillable=1)
-    with raises(TypeError):
-        Asset(updatable=1)
-    with raises(TypeError):
-        Asset(data='we need more lemon pledge')
+        asset.validate_asset(amount='a')
diff --git a/tests/common/test_transaction.py b/tests/common/test_transaction.py
index 5f2d58fb..baba35af 100644
--- a/tests/common/test_transaction.py
+++ b/tests/common/test_transaction.py
@@ -1,4 +1,5 @@
-from pytest import raises, mark
+from pytest import raises
+from unittest.mock import patch
 
 
 def test_fulfillment_serialization(ffill_uri, user_pub):
@@ -166,29 +167,7 @@ def test_generate_conditions_split_half_recursive(user_pub, user2_pub,
     expected_threshold.add_subfulfillment(expected_simple3)
     expected.add_subfulfillment(expected_threshold)
 
-    cond = Condition.generate([user_pub, [user2_pub, expected_simple3]])
-    assert cond.fulfillment.to_dict() == expected.to_dict()
-
-
-def test_generate_conditions_split_half_recursive_custom_threshold(user_pub,
-                                                                   user2_pub,
-                                                                   user3_pub):
-    from bigchaindb.common.transaction import Condition
-    from cryptoconditions import Ed25519Fulfillment, ThresholdSha256Fulfillment
-
-    expected_simple1 = Ed25519Fulfillment(public_key=user_pub)
-    expected_simple2 = Ed25519Fulfillment(public_key=user2_pub)
-    expected_simple3 = Ed25519Fulfillment(public_key=user3_pub)
-
-    expected = ThresholdSha256Fulfillment(threshold=1)
-    expected.add_subfulfillment(expected_simple1)
-    expected_threshold = ThresholdSha256Fulfillment(threshold=1)
-    expected_threshold.add_subfulfillment(expected_simple2)
-    expected_threshold.add_subfulfillment(expected_simple3)
-    expected.add_subfulfillment(expected_threshold)
-
-    cond = Condition.generate(([user_pub, ([user2_pub, expected_simple3], 1)],
-                              1))
+    cond = Condition.generate([user_pub, [user2_pub, expected_simple3]], 1)
     assert cond.fulfillment.to_dict() == expected.to_dict()
 
 
@@ -208,7 +187,7 @@ def test_generate_conditions_split_half_single_owner(user_pub, user2_pub,
     expected.add_subfulfillment(expected_threshold)
     expected.add_subfulfillment(expected_simple1)
 
-    cond = Condition.generate([[expected_simple2, user3_pub], user_pub])
+    cond = Condition.generate([[expected_simple2, user3_pub], user_pub], 1)
     assert cond.fulfillment.to_dict() == expected.to_dict()
 
 
@@ -225,7 +204,7 @@ def test_generate_conditions_flat_ownage(user_pub, user2_pub, user3_pub):
     expected.add_subfulfillment(expected_simple2)
     expected.add_subfulfillment(expected_simple3)
 
-    cond = Condition.generate([user_pub, user2_pub, expected_simple3])
+    cond = Condition.generate([user_pub, user2_pub, expected_simple3], 1)
     assert cond.fulfillment.to_dict() == expected.to_dict()
 
 
@@ -234,7 +213,7 @@ def test_generate_conditions_single_owner(user_pub):
     from cryptoconditions import Ed25519Fulfillment
 
     expected = Ed25519Fulfillment(public_key=user_pub)
-    cond = Condition.generate([user_pub])
+    cond = Condition.generate([user_pub], 1)
 
     assert cond.fulfillment.to_dict() == expected.to_dict()
 
@@ -244,48 +223,23 @@ def test_generate_conditions_single_owner_with_condition(user_pub):
     from cryptoconditions import Ed25519Fulfillment
 
     expected = Ed25519Fulfillment(public_key=user_pub)
-    cond = Condition.generate([expected])
+    cond = Condition.generate([expected], 1)
 
     assert cond.fulfillment.to_dict() == expected.to_dict()
 
 
-# TODO FOR CC: see skip reason
-@mark.skip(reason='threshold(hashlock).to_dict() exposes secret')
-def test_generate_threshold_condition_with_hashlock(user_pub, user2_pub,
-                                                    user3_pub):
-    from bigchaindb.common.transaction import Condition
-    from cryptoconditions import (PreimageSha256Fulfillment,
-                                  Ed25519Fulfillment,
-                                  ThresholdSha256Fulfillment)
-
-    secret = b'much secret, wow'
-    hashlock = PreimageSha256Fulfillment(preimage=secret)
-
-    expected_simple1 = Ed25519Fulfillment(public_key=user_pub)
-    expected_simple3 = Ed25519Fulfillment(public_key=user3_pub)
-
-    expected = ThresholdSha256Fulfillment(threshold=2)
-    expected_sub = ThresholdSha256Fulfillment(threshold=2)
-    expected_sub.add_subfulfillment(expected_simple1)
-    expected_sub.add_subfulfillment(hashlock)
-    expected.add_subfulfillment(expected_simple3)
-
-    cond = Condition.generate([[user_pub, hashlock], expected_simple3])
-    assert cond.fulfillment.to_dict() == expected.to_dict()
-
-
 def test_generate_conditions_invalid_parameters(user_pub, user2_pub,
                                                 user3_pub):
     from bigchaindb.common.transaction import Condition
 
     with raises(ValueError):
-        Condition.generate([])
+        Condition.generate([], 1)
     with raises(TypeError):
-        Condition.generate('not a list')
+        Condition.generate('not a list', 1)
     with raises(ValueError):
-        Condition.generate([[user_pub, [user2_pub, [user3_pub]]]])
+        Condition.generate([[user_pub, [user2_pub, [user3_pub]]]], 1)
     with raises(ValueError):
-        Condition.generate([[user_pub]])
+        Condition.generate([[user_pub]], 1)
 
 
 def test_invalid_transaction_initialization():
@@ -321,7 +275,8 @@ def test_invalid_transaction_initialization():
 def test_create_default_asset_on_tx_initialization():
     from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction(Transaction.CREATE, None)
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction(Transaction.CREATE, None)
     expected = Asset()
     asset = tx.asset
 
@@ -510,10 +465,62 @@ def test_cast_transaction_link_to_boolean():
     assert bool(TransactionLink(False, False)) is True
 
 
+def test_asset_link_serialization():
+    from bigchaindb.common.transaction import AssetLink
+
+    data_id = 'a asset id'
+    expected = {
+        'id': data_id,
+    }
+    asset_link = AssetLink(data_id)
+
+    assert asset_link.to_dict() == expected
+
+
+def test_asset_link_serialization_with_empty_payload():
+    from bigchaindb.common.transaction import AssetLink
+
+    expected = None
+    asset_link = AssetLink()
+
+    assert asset_link.to_dict() == expected
+
+
+def test_asset_link_deserialization():
+    from bigchaindb.common.transaction import AssetLink
+
+    data_id = 'a asset id'
+    expected = AssetLink(data_id)
+    asset_link = {
+        'id': data_id
+    }
+    asset_link = AssetLink.from_dict(asset_link)
+
+    assert asset_link == expected
+
+
+def test_asset_link_deserialization_with_empty_payload():
+    from bigchaindb.common.transaction import AssetLink
+
+    expected = AssetLink()
+    asset_link = AssetLink.from_dict(None)
+
+    assert asset_link == expected
+
+
+def test_cast_asset_link_to_boolean():
+    from bigchaindb.common.transaction import AssetLink
+
+    assert bool(AssetLink()) is False
+    assert bool(AssetLink('a')) is True
+    assert bool(AssetLink(False)) is True
+
+
 def test_add_fulfillment_to_tx(user_ffill):
     from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction(Transaction.CREATE, Asset(), [], [])
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction(Transaction.CREATE, Asset(), [], [])
     tx.add_fulfillment(user_ffill)
 
     assert len(tx.fulfillments) == 1
@@ -522,7 +529,8 @@ def test_add_fulfillment_to_tx(user_ffill):
 def test_add_fulfillment_to_tx_with_invalid_parameters():
     from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction(Transaction.CREATE, Asset())
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction(Transaction.CREATE, Asset())
     with raises(TypeError):
         tx.add_fulfillment('somewronginput')
 
@@ -530,7 +538,8 @@ def test_add_fulfillment_to_tx_with_invalid_parameters():
 def test_add_condition_to_tx(user_cond):
     from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction(Transaction.CREATE, Asset())
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction(Transaction.CREATE, Asset())
     tx.add_condition(user_cond)
 
     assert len(tx.conditions) == 1
@@ -539,7 +548,8 @@ def test_add_condition_to_tx(user_cond):
 def test_add_condition_to_tx_with_invalid_parameters():
     from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction(Transaction.CREATE, Asset(), [], [])
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction(Transaction.CREATE, Asset(), [], [])
     with raises(TypeError):
         tx.add_condition('somewronginput')
 
@@ -614,16 +624,14 @@ def test_validate_multiple_fulfillments(user_ffill, user_cond, user_priv):
     from bigchaindb.common.crypto import SigningKey
     from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction(Transaction.CREATE, Asset(),
+    tx = Transaction(Transaction.CREATE, Asset(divisible=True),
                      [user_ffill, deepcopy(user_ffill)],
-                     [user_ffill, deepcopy(user_cond)])
+                     [user_cond, deepcopy(user_cond)])
 
     expected_first = deepcopy(tx)
     expected_second = deepcopy(tx)
     expected_first.fulfillments = [expected_first.fulfillments[0]]
-    expected_first.conditions = [expected_first.conditions[0]]
     expected_second.fulfillments = [expected_second.fulfillments[1]]
-    expected_second.conditions = [expected_second.conditions[1]]
 
     expected_first_bytes = str(expected_first).encode()
     expected_first.fulfillments[0].fulfillment.sign(expected_first_bytes,
@@ -674,7 +682,7 @@ def test_multiple_fulfillment_validation_of_transfer_tx(user_ffill, user_cond,
                                                Fulfillment, Condition, Asset)
     from cryptoconditions import Ed25519Fulfillment
 
-    tx = Transaction(Transaction.CREATE, Asset(),
+    tx = Transaction(Transaction.CREATE, Asset(divisible=True),
                      [user_ffill, deepcopy(user_ffill)],
                      [user_cond, deepcopy(user_cond)])
     tx.sign([user_priv])
@@ -715,10 +723,6 @@ def test_validate_fulfillments_of_transfer_tx_with_invalid_params(transfer_tx,
     with raises(TypeError):
         transfer_tx.operation = "Operation that doesn't exist"
         transfer_tx.fulfillments_valid([utx.conditions[0]])
-    with raises(ValueError):
-        tx = utx.sign([user_priv])
-        tx.conditions = []
-        tx.fulfillments_valid()
 
 
 def test_create_create_transaction_single_io(user_cond, user_pub, data,
@@ -754,7 +758,8 @@ def test_create_create_transaction_single_io(user_cond, user_pub, data,
     }
 
     asset = Asset(data, data_id)
-    tx = Transaction.create([user_pub], [user_pub], data, asset).to_dict()
+    tx = Transaction.create([user_pub], [([user_pub], 1)],
+                            data, asset).to_dict()
     tx.pop('id')
     tx['transaction']['metadata'].pop('id')
     tx['transaction'].pop('timestamp')
@@ -766,17 +771,20 @@ def test_create_create_transaction_single_io(user_cond, user_pub, data,
 def test_validate_single_io_create_transaction(user_pub, user_priv, data):
     from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction.create([user_pub], [user_pub], data, Asset())
+    tx = Transaction.create([user_pub], [([user_pub], 1)], data, Asset())
     tx = tx.sign([user_priv])
     assert tx.fulfillments_valid() is True
 
 
-@mark.skip(reason='Multiple inputs and outputs in CREATE not supported')
-# TODO: Add digital assets
 def test_create_create_transaction_multiple_io(user_cond, user2_cond, user_pub,
                                                user2_pub):
-    from bigchaindb.common.transaction import Transaction
+    from bigchaindb.common.transaction import Transaction, Asset, Fulfillment
 
+    # a fulfillment for a create transaction with multiple `owners_before`
+    # is a fulfillment for an implicit threshold condition with
+    # weight = len(owners_before)
+    ffill = Fulfillment.generate([user_pub, user2_pub]).to_dict()
+    ffill.update({'fid': 0})
     expected = {
         'transaction': {
             'conditions': [user_cond.to_dict(0), user2_cond.to_dict(1)],
@@ -785,45 +793,32 @@ def test_create_create_transaction_multiple_io(user_cond, user2_cond, user_pub,
                     'message': 'hello'
                 }
             },
-            'fulfillments': [
-                {
-                    'owners_before': [
-                        user_pub,
-                    ],
-                    'fid': 0,
-                    'fulfillment': None,
-                    'input': None
-                },
-                {
-                    'owners_before': [
-                        user2_pub,
-                    ],
-                    'fid': 1,
-                    'fulfillment': None,
-                    'input': None
-                }
-            ],
+            'fulfillments': [ffill],
             'operation': 'CREATE',
         },
         'version': 1
     }
-    tx = Transaction.create([user_pub, user2_pub], [user_pub, user2_pub],
-                            {'message': 'hello'}).to_dict()
+    asset = Asset(divisible=True)
+    tx = Transaction.create([user_pub, user2_pub],
+                            [([user_pub], 1), ([user2_pub], 1)],
+                            asset=asset,
+                            metadata={'message': 'hello'}).to_dict()
     tx.pop('id')
     tx['transaction']['metadata'].pop('id')
     tx['transaction'].pop('timestamp')
+    tx['transaction'].pop('asset')
 
     assert tx == expected
 
 
-@mark.skip(reason='Multiple inputs and outputs in CREATE not supported')
-# TODO: Add digital assets
 def test_validate_multiple_io_create_transaction(user_pub, user_priv,
                                                  user2_pub, user2_priv):
-    from bigchaindb.common.transaction import Transaction
+    from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction.create([user_pub, user2_pub], [user_pub, user2_pub],
-                            {'message': 'hello'})
+    tx = Transaction.create([user_pub, user2_pub],
+                            [([user_pub], 1), ([user2_pub], 1)],
+                            metadata={'message': 'hello'},
+                            asset=Asset(divisible=True))
     tx = tx.sign([user_priv, user2_priv])
     assert tx.fulfillments_valid() is True
 
@@ -862,7 +857,8 @@ def test_create_create_transaction_threshold(user_pub, user2_pub, user3_pub,
         'version': 1
     }
     asset = Asset(data, data_id)
-    tx = Transaction.create([user_pub], [user_pub, user2_pub], data, asset)
+    tx = Transaction.create([user_pub], [([user_pub, user2_pub], 1)],
+                            data, asset)
     tx_dict = tx.to_dict()
     tx_dict.pop('id')
     tx_dict['transaction']['metadata'].pop('id')
@@ -876,80 +872,27 @@ def test_validate_threshold_create_transaction(user_pub, user_priv, user2_pub,
                                                data):
     from bigchaindb.common.transaction import Transaction, Asset
 
-    tx = Transaction.create([user_pub], [user_pub, user2_pub], data, Asset())
+    tx = Transaction.create([user_pub], [([user_pub, user2_pub], 1)],
+                            data, Asset())
     tx = tx.sign([user_priv])
     assert tx.fulfillments_valid() is True
 
 
-def test_create_create_transaction_hashlock(user_pub, data, data_id):
-    from cryptoconditions import PreimageSha256Fulfillment
-    from bigchaindb.common.transaction import Transaction, Condition, Asset
-
-    secret = b'much secret, wow'
-    hashlock = PreimageSha256Fulfillment(preimage=secret).condition_uri
-    cond = Condition(hashlock)
-
-    expected = {
-        'transaction': {
-            'conditions': [cond.to_dict(0)],
-            'metadata': {
-                'data': data,
-            },
-            'asset': {
-                'id': data_id,
-                'divisible': False,
-                'updatable': False,
-                'refillable': False,
-                'data': data,
-            },
-            'fulfillments': [
-                {
-                    'owners_before': [
-                        user_pub,
-                    ],
-                    'fid': 0,
-                    'fulfillment': None,
-                    'input': None
-                },
-            ],
-            'operation': 'CREATE',
-        },
-        'version': 1
-    }
-
-    asset = Asset(data, data_id)
-    tx = Transaction.create([user_pub], [], data, asset, secret).to_dict()
-    tx.pop('id')
-    tx['transaction']['metadata'].pop('id')
-    tx['transaction'].pop('timestamp')
-    tx['transaction']['fulfillments'][0]['fulfillment'] = None
-
-    assert tx == expected
-
-
-def test_validate_hashlock_create_transaction(user_pub, user_priv, data):
-    from bigchaindb.common.transaction import Transaction, Asset
-
-    tx = Transaction.create([user_pub], [], data, Asset(), b'much secret, wow')
-    tx = tx.sign([user_priv])
-    assert tx.fulfillments_valid() is True
-
-
-def test_create_create_transaction_with_invalid_parameters():
+def test_create_create_transaction_with_invalid_parameters(user_pub):
     from bigchaindb.common.transaction import Transaction
 
     with raises(TypeError):
         Transaction.create('not a list')
     with raises(TypeError):
         Transaction.create([], 'not a list')
-    with raises(NotImplementedError):
-        Transaction.create(['a', 'b'], ['c', 'd'])
-    with raises(NotImplementedError):
-        Transaction.create(['a'], [], time_expire=123)
     with raises(ValueError):
-        Transaction.create(['a'], [], secret=None)
+        Transaction.create([], [user_pub])
     with raises(ValueError):
-        Transaction.create([], [], secret='wow, much secret')
+        Transaction.create([user_pub], [])
+    with raises(ValueError):
+        Transaction.create([user_pub], [user_pub])
+    with raises(ValueError):
+        Transaction.create([user_pub], [([user_pub],)])
 
 
 def test_conditions_to_inputs(tx):
@@ -995,7 +938,7 @@ def test_create_transfer_transaction_single_io(tx, user_pub, user2_pub,
     }
     inputs = tx.to_inputs([0])
     asset = Asset(None, data_id)
-    transfer_tx = Transaction.transfer(inputs, [user2_pub], asset=asset)
+    transfer_tx = Transaction.transfer(inputs, [([user2_pub], 1)], asset=asset)
     transfer_tx = transfer_tx.sign([user_priv])
     transfer_tx = transfer_tx.to_dict()
     transfer_tx_body = transfer_tx['transaction']
@@ -1014,16 +957,15 @@ def test_create_transfer_transaction_single_io(tx, user_pub, user2_pub,
     assert transfer_tx.fulfillments_valid([tx.conditions[0]]) is True
 
 
-@mark.skip(reason='FIXME: When divisible assets land')
 def test_create_transfer_transaction_multiple_io(user_pub, user_priv,
                                                  user2_pub, user2_priv,
                                                  user3_pub, user2_cond):
-    from bigchaindb.common.transaction import Transaction
+    from bigchaindb.common.transaction import Transaction, Asset
 
-    tx1 = Transaction.create([user_pub], [user_pub], {'message': 'hello'})
-    tx1 = tx1.sign([user_priv])
-    tx2 = Transaction.create([user2_pub], [user2_pub], {'message': 'hello'})
-    tx2 = tx2.sign([user2_priv])
+    asset = Asset(divisible=True)
+    tx = Transaction.create([user_pub], [([user_pub], 1), ([user2_pub], 1)],
+                            asset=asset, metadata={'message': 'hello'})
+    tx = tx.sign([user_priv])
 
     expected = {
         'transaction': {
@@ -1037,7 +979,7 @@ def test_create_transfer_transaction_multiple_io(user_pub, user_priv,
                     'fid': 0,
                     'fulfillment': None,
                     'input': {
-                        'txid': tx1.id,
+                        'txid': tx.id,
                         'cid': 0
                     }
                 }, {
@@ -1047,8 +989,8 @@ def test_create_transfer_transaction_multiple_io(user_pub, user_priv,
                     'fid': 1,
                     'fulfillment': None,
                     'input': {
-                        'txid': tx2.id,
-                        'cid': 0
+                        'txid': tx.id,
+                        'cid': 1
                     }
                 }
             ],
@@ -1056,30 +998,28 @@ def test_create_transfer_transaction_multiple_io(user_pub, user_priv,
         },
         'version': 1
     }
-    tx1_inputs = tx1.to_inputs()
-    tx2_inputs = tx2.to_inputs()
-    tx_inputs = tx1_inputs + tx2_inputs
 
-    transfer_tx = Transaction.transfer(tx_inputs, [[user2_pub], [user2_pub]])
+    transfer_tx = Transaction.transfer(tx.to_inputs(),
+                                       [([user2_pub], 1), ([user2_pub], 1)],
+                                       asset=tx.asset)
     transfer_tx = transfer_tx.sign([user_priv, user2_priv])
-    transfer_tx = transfer_tx
 
     assert len(transfer_tx.fulfillments) == 2
     assert len(transfer_tx.conditions) == 2
 
-    combined_conditions = tx1.conditions + tx2.conditions
-    assert transfer_tx.fulfillments_valid(combined_conditions) is True
+    assert transfer_tx.fulfillments_valid(tx.conditions) is True
 
     transfer_tx = transfer_tx.to_dict()
     transfer_tx['transaction']['fulfillments'][0]['fulfillment'] = None
     transfer_tx['transaction']['fulfillments'][1]['fulfillment'] = None
     transfer_tx['transaction'].pop('timestamp')
     transfer_tx.pop('id')
+    transfer_tx['transaction'].pop('asset')
 
     assert expected == transfer_tx
 
 
-def test_create_transfer_with_invalid_parameters():
+def test_create_transfer_with_invalid_parameters(user_pub):
     from bigchaindb.common.transaction import Transaction, Asset
 
     with raises(TypeError):
@@ -1090,17 +1030,25 @@ def test_create_transfer_with_invalid_parameters():
         Transaction.transfer(['fulfillment'], {}, Asset())
     with raises(ValueError):
         Transaction.transfer(['fulfillment'], [], Asset())
+    with raises(ValueError):
+        Transaction.transfer(['fulfillment'], [user_pub], Asset())
+    with raises(ValueError):
+        Transaction.transfer(['fulfillment'], [([user_pub],)], Asset())
 
 
 def test_cant_add_empty_condition():
-    from bigchaindb.common.transaction import Transaction
-    tx = Transaction(Transaction.CREATE, None)
+    from bigchaindb.common.transaction import Transaction, Asset
+
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction(Transaction.CREATE, None)
     with raises(TypeError):
         tx.add_condition(None)
 
 
 def test_cant_add_empty_fulfillment():
-    from bigchaindb.common.transaction import Transaction
-    tx = Transaction(Transaction.CREATE, None)
+    from bigchaindb.common.transaction import Transaction, Asset
+
+    with patch.object(Asset, 'validate_asset', return_value=None):
+        tx = Transaction(Transaction.CREATE, None)
     with raises(TypeError):
         tx.add_fulfillment(None)
diff --git a/tests/conftest.py b/tests/conftest.py
index 58178b7f..fcb6b318 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -72,7 +72,7 @@ def b(request, node_config):
 @pytest.fixture
 def create_tx(b, user_vk):
     from bigchaindb.models import Transaction
-    return Transaction.create([b.me], [user_vk])
+    return Transaction.create([b.me], [([user_vk], 1)])
 
 
 @pytest.fixture
@@ -84,5 +84,5 @@ def signed_create_tx(b, create_tx):
 def signed_transfer_tx(signed_create_tx, user_vk, user_sk):
     from bigchaindb.models import Transaction
     inputs = signed_create_tx.to_inputs()
-    tx = Transaction.transfer(inputs, [user_vk], signed_create_tx.asset)
+    tx = Transaction.transfer(inputs, [([user_vk], 1)], signed_create_tx.asset)
     return tx.sign([user_sk])
diff --git a/tests/db/conftest.py b/tests/db/conftest.py
index f55a4c34..43a352a9 100644
--- a/tests/db/conftest.py
+++ b/tests/db/conftest.py
@@ -10,11 +10,13 @@ import pytest
 import rethinkdb as r
 
 from bigchaindb import Bigchain
-from bigchaindb.db import get_conn
+from bigchaindb.db import get_conn, init_database
 from bigchaindb.common import crypto
+from bigchaindb.common.exceptions import DatabaseAlreadyExists
 
 USER2_SK, USER2_VK = crypto.generate_key_pair()
 
+
 @pytest.fixture(autouse=True)
 def restore_config(request, node_config):
     from bigchaindb import config_utils
@@ -25,53 +27,17 @@ def restore_config(request, node_config):
 def setup_database(request, node_config):
     print('Initializing test db')
     db_name = node_config['database']['name']
-    get_conn().repl()
+    conn = get_conn()
+
+    if r.db_list().contains(db_name).run(conn):
+        r.db_drop(db_name).run(conn)
+
     try:
-        r.db_create(db_name).run()
-    except r.ReqlOpFailedError as e:
-        if e.message == 'Database `{}` already exists.'.format(db_name):
-            r.db_drop(db_name).run()
-            r.db_create(db_name).run()
-        else:
-            raise
+        init_database()
+    except DatabaseAlreadyExists:
+        print('Database already exists.')
 
-    print('Finished initializing test db')
-
-    # setup tables
-    r.db(db_name).table_create('bigchain').run()
-    r.db(db_name).table_create('backlog').run()
-    r.db(db_name).table_create('votes').run()
-
-    # create the secondary indexes
-    # to order blocks by timestamp
-    r.db(db_name).table('bigchain').index_create('block_timestamp', r.row['block']['timestamp']).run()
-    # to order blocks by block number
-    r.db(db_name).table('bigchain').index_create('block_number', r.row['block']['block_number']).run()
-    # to order transactions by timestamp
-    r.db(db_name).table('backlog').index_create('transaction_timestamp', r.row['transaction']['timestamp']).run()
-    # to query by payload uuid
-    r.db(db_name).table('bigchain').index_create(
-        'metadata_id',
-        r.row['block']['transactions']['transaction']['metadata']['id'],
-        multi=True,
-    ).run()
-    # compound index to read transactions from the backlog per assignee
-    r.db(db_name).table('backlog')\
-        .index_create('assignee__transaction_timestamp', [r.row['assignee'], r.row['transaction']['timestamp']])\
-        .run()
-    # compound index to order votes by block id and node
-    r.db(db_name).table('votes').index_create('block_and_voter',
-                                              [r.row['vote']['voting_for_block'], r.row['node_pubkey']]).run()
-    # secondary index for asset uuid
-    r.db(db_name).table('bigchain')\
-                .index_create('asset_id',
-                              r.row['block']['transactions']['transaction']['asset']['id'], multi=True)\
-                .run()
-    # order transactions by id
-    r.db(db_name).table('bigchain').index_create('transaction_id', r.row['block']['transactions']['id'],
-                                                 multi=True).run()
-
-    r.db(db_name).table('bigchain').index_wait('transaction_id').run()
+    print('Finishing init database')
 
     def fin():
         print('Deleting `{}` database'.format(db_name))
@@ -81,7 +47,6 @@ def setup_database(request, node_config):
         except r.ReqlOpFailedError as e:
             if e.message != 'Database `{}` does not exist.'.format(db_name):
                 raise
-
         print('Finished deleting `{}`'.format(db_name))
 
     request.addfinalizer(fin)
@@ -119,7 +84,7 @@ def inputs(user_vk):
     prev_block_id = g.id
     for block in range(4):
         transactions = [
-            Transaction.create([b.me], [user_vk]).sign([b.me_private])
+            Transaction.create([b.me], [([user_vk], 1)]).sign([b.me_private])
             for i in range(10)
         ]
         block = b.create_block(transactions)
diff --git a/tests/db/test_bigchain_api.py b/tests/db/test_bigchain_api.py
index b52dd3a7..144bfeed 100644
--- a/tests/db/test_bigchain_api.py
+++ b/tests/db/test_bigchain_api.py
@@ -15,7 +15,7 @@ def dummy_tx():
     import bigchaindb
     from bigchaindb.models import Transaction
     b = bigchaindb.Bigchain()
-    tx = Transaction.create([b.me], [b.me])
+    tx = Transaction.create([b.me], [([b.me], 1)])
     tx = tx.sign([b.me_private])
     return tx
 
@@ -37,7 +37,7 @@ class TestBigchainApi(object):
 
         b.create_genesis_block()
 
-        tx = Transaction.create([b.me], [b.me])
+        tx = Transaction.create([b.me], [([b.me], 1)])
         tx = tx.sign([b.me_private])
         monkeypatch.setattr('time.time', lambda: 1)
         block1 = b.create_block([tx])
@@ -60,7 +60,7 @@ class TestBigchainApi(object):
 
         b.create_genesis_block()
 
-        tx = Transaction.create([b.me], [b.me])
+        tx = Transaction.create([b.me], [([b.me], 1)])
         tx = tx.sign([b.me_private])
         block1 = b.create_block([tx])
 
@@ -74,7 +74,7 @@ class TestBigchainApi(object):
 
         b.create_genesis_block()
 
-        tx = Transaction.create([b.me], [b.me])
+        tx = Transaction.create([b.me], [([b.me], 1)])
         tx = tx.sign([b.me_private])
 
         monkeypatch.setattr('time.time', lambda: 1)
@@ -99,7 +99,7 @@ class TestBigchainApi(object):
 
         b.create_genesis_block()
 
-        tx = Transaction.create([b.me], [b.me])
+        tx = Transaction.create([b.me], [([b.me], 1)])
         tx = tx.sign([b.me_private])
 
         monkeypatch.setattr('time.time', lambda: 1)
@@ -107,13 +107,15 @@ class TestBigchainApi(object):
         b.write_block(block1, durability='hard')
 
         monkeypatch.setattr('time.time', lambda: 2)
-        transfer_tx = Transaction.transfer(tx.to_inputs(), [b.me], tx.asset)
+        transfer_tx = Transaction.transfer(tx.to_inputs(), [([b.me], 1)],
+                                           tx.asset)
         transfer_tx = transfer_tx.sign([b.me_private])
         block2 = b.create_block([transfer_tx])
         b.write_block(block2, durability='hard')
 
         monkeypatch.setattr('time.time', lambda: 3)
-        transfer_tx2 = Transaction.transfer(tx.to_inputs(), [b.me], tx.asset)
+        transfer_tx2 = Transaction.transfer(tx.to_inputs(), [([b.me], 1)],
+                                            tx.asset)
         transfer_tx2 = transfer_tx2.sign([b.me_private])
         block3 = b.create_block([transfer_tx2])
         b.write_block(block3, durability='hard')
@@ -133,7 +135,7 @@ class TestBigchainApi(object):
 
         b.create_genesis_block()
 
-        tx = Transaction.create([b.me], [b.me])
+        tx = Transaction.create([b.me], [([b.me], 1)])
         tx = tx.sign([b.me_private])
 
         monkeypatch.setattr('time.time', lambda: 1)
@@ -159,13 +161,13 @@ class TestBigchainApi(object):
         b.create_genesis_block()
 
         monkeypatch.setattr('time.time', lambda: 1)
-        tx1 = Transaction.create([b.me], [b.me])
+        tx1 = Transaction.create([b.me], [([b.me], 1)])
         tx1 = tx1.sign([b.me_private])
         block1 = b.create_block([tx1])
         b.write_block(block1, durability='hard')
 
         monkeypatch.setattr('time.time', lambda: 2)
-        tx2 = Transaction.create([b.me], [b.me])
+        tx2 = Transaction.create([b.me], [([b.me], 1)])
         tx2 = tx2.sign([b.me_private])
         block2 = b.create_block([tx2])
         b.write_block(block2, durability='hard')
@@ -185,7 +187,7 @@ class TestBigchainApi(object):
         from bigchaindb.models import Transaction
 
         metadata = {'msg': 'Hello BigchainDB!'}
-        tx = Transaction.create([b.me], [user_vk], metadata=metadata)
+        tx = Transaction.create([b.me], [([user_vk], 1)], metadata=metadata)
 
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -205,7 +207,7 @@ class TestBigchainApi(object):
         input_tx = b.get_owned_ids(user_vk).pop()
         input_tx = b.get_transaction(input_tx.txid)
         inputs = input_tx.to_inputs()
-        tx = Transaction.transfer(inputs, [user_vk], input_tx.asset)
+        tx = Transaction.transfer(inputs, [([user_vk], 1)], input_tx.asset)
         tx = tx.sign([user_sk])
         response = b.write_transaction(tx)
 
@@ -223,7 +225,7 @@ class TestBigchainApi(object):
         input_tx = b.get_owned_ids(user_vk).pop()
         input_tx = b.get_transaction(input_tx.txid)
         inputs = input_tx.to_inputs()
-        tx = Transaction.transfer(inputs, [user_vk], input_tx.asset)
+        tx = Transaction.transfer(inputs, [([user_vk], 1)], input_tx.asset)
         tx = tx.sign([user_sk])
         b.write_transaction(tx)
 
@@ -243,9 +245,9 @@ class TestBigchainApi(object):
         input_tx = b.get_owned_ids(user_vk).pop()
         input_tx = b.get_transaction(input_tx.txid)
         inputs = input_tx.to_inputs()
-        tx = Transaction.transfer(inputs, [user_vk], input_tx.asset)
+        tx = Transaction.transfer(inputs, [([user_vk], 1)], input_tx.asset)
         tx = tx.sign([user_sk])
-        b.write_transaction(tx)
+        # There's no need to b.write_transaction(tx) to the backlog
 
         # create block
         block = b.create_block([tx])
@@ -257,8 +259,37 @@ class TestBigchainApi(object):
         response = b.get_transaction(tx.id)
 
         # should be None, because invalid blocks are ignored
+        # and a copy of the tx is not in the backlog
         assert response is None
 
+    @pytest.mark.usefixtures('inputs')
+    def test_read_transaction_invalid_block_and_backlog(self, b, user_vk, user_sk):
+        from bigchaindb.models import Transaction
+
+        input_tx = b.get_owned_ids(user_vk).pop()
+        input_tx = b.get_transaction(input_tx.txid)
+        inputs = input_tx.to_inputs()
+        tx = Transaction.transfer(inputs, [([user_vk], 1)], input_tx.asset)
+        tx = tx.sign([user_sk])
+
+        # Make sure there's a copy of tx in the backlog
+        b.write_transaction(tx)
+
+        # create block
+        block = b.create_block([tx])
+        b.write_block(block, durability='hard')
+
+        # vote the block invalid
+        vote = b.vote(block.id, b.get_last_voted_block().id, False)
+        b.write_vote(vote)
+
+        # a copy of the tx is both in the backlog and in an invalid
+        # block, so get_transaction should return a transaction,
+        # and a status of TX_IN_BACKLOG
+        response, status = b.get_transaction(tx.id, include_status=True)
+        assert tx.to_dict() == response.to_dict()
+        assert status == b.TX_IN_BACKLOG
+
     @pytest.mark.usefixtures('inputs')
     def test_genesis_block(self, b):
         import rethinkdb as r
@@ -340,6 +371,15 @@ class TestBigchainApi(object):
 
         assert excinfo.value.args[0] == 'Empty block creation is not allowed'
 
+    @pytest.mark.usefixtures('inputs')
+    def test_get_block_by_id(self, b):
+        new_block = dummy_block()
+        b.write_block(new_block, durability='hard')
+
+        assert b.get_block(new_block.id) == new_block.to_dict()
+        block, status = b.get_block(new_block.id, include_status=True)
+        assert status == b.BLOCK_UNDECIDED
+
     def test_get_last_voted_block_returns_genesis_if_no_votes_has_been_casted(self, b):
         import rethinkdb as r
         from bigchaindb import util
@@ -499,7 +539,7 @@ class TestBigchainApi(object):
         input_tx = b.get_owned_ids(user_vk).pop()
         input_tx = b.get_transaction(input_tx.txid)
         inputs = input_tx.to_inputs()
-        tx = Transaction.transfer(inputs, [user_vk], input_tx.asset)
+        tx = Transaction.transfer(inputs, [([user_vk], 1)], input_tx.asset)
         tx = tx.sign([user_sk])
         b.write_transaction(tx)
 
@@ -525,7 +565,7 @@ class TestBigchainApi(object):
             input_tx = b.get_owned_ids(user_vk).pop()
             input_tx = b.get_transaction(input_tx.txid)
             inputs = input_tx.to_inputs()
-            tx = Transaction.transfer(inputs, [user_vk], input_tx.asset)
+            tx = Transaction.transfer(inputs, [([user_vk], 1)], input_tx.asset)
             tx = tx.sign([user_sk])
             b.write_transaction(tx)
 
@@ -549,11 +589,21 @@ class TestBigchainApi(object):
         fulfillment = Fulfillment(Ed25519Fulfillment(public_key=user_vk),
                                   [user_vk],
                                   TransactionLink('somethingsomething', 0))
-        tx = Transaction.transfer([fulfillment], [user_vk], Asset())
+        tx = Transaction.transfer([fulfillment], [([user_vk], 1)], Asset())
 
-        with pytest.raises(TransactionDoesNotExist) as excinfo:
+        with pytest.raises(TransactionDoesNotExist):
             tx.validate(Bigchain())
 
+    def test_count_backlog(self, b, user_vk):
+        from bigchaindb.models import Transaction
+
+        for _ in range(4):
+            tx = Transaction.create([b.me],
+                                    [([user_vk], 1)]).sign([b.me_private])
+            b.write_transaction(tx)
+
+        assert b.backend.count_backlog() == 4
+
 
 class TestTransactionValidation(object):
     def test_create_operation_with_inputs(self, b, user_vk, create_tx):
@@ -591,7 +641,7 @@ class TestTransactionValidation(object):
         input_tx = b.get_owned_ids(user_vk).pop()
         input_transaction = b.get_transaction(input_tx.txid)
         sk, vk = generate_key_pair()
-        tx = Transaction.create([vk], [user_vk])
+        tx = Transaction.create([vk], [([user_vk], 1)])
         tx.operation = 'TRANSFER'
         tx.asset = input_transaction.asset
         tx.fulfillments[0].tx_input = input_tx
@@ -635,7 +685,8 @@ class TestTransactionValidation(object):
         input_tx = b.get_owned_ids(user_vk).pop()
         input_tx = b.get_transaction(input_tx.txid)
         inputs = input_tx.to_inputs()
-        transfer_tx = Transaction.transfer(inputs, [user_vk], input_tx.asset)
+        transfer_tx = Transaction.transfer(inputs, [([user_vk], 1)],
+                                           input_tx.asset)
         transfer_tx = transfer_tx.sign([user_sk])
 
         assert transfer_tx == b.validate_transaction(transfer_tx)
@@ -659,7 +710,8 @@ class TestTransactionValidation(object):
         inputs = input_tx.to_inputs()
 
         # create a transaction that's valid but not in a voted valid block
-        transfer_tx = Transaction.transfer(inputs, [user_vk], input_tx.asset)
+        transfer_tx = Transaction.transfer(inputs, [([user_vk], 1)],
+                                           input_tx.asset)
         transfer_tx = transfer_tx.sign([user_sk])
 
         assert transfer_tx == b.validate_transaction(transfer_tx)
@@ -669,8 +721,9 @@ class TestTransactionValidation(object):
         b.write_block(block, durability='hard')
 
         # create transaction with the undecided input
-        tx_invalid = Transaction.transfer(transfer_tx.to_inputs(), [user_vk],
-                                         transfer_tx.asset)
+        tx_invalid = Transaction.transfer(transfer_tx.to_inputs(),
+                                          [([user_vk], 1)],
+                                          transfer_tx.asset)
         tx_invalid = tx_invalid.sign([user_sk])
 
         with pytest.raises(TransactionNotInValidBlock):
@@ -768,7 +821,7 @@ class TestMultipleInputs(object):
         tx_link = b.get_owned_ids(user_vk).pop()
         input_tx = b.get_transaction(tx_link.txid)
         inputs = input_tx.to_inputs()
-        tx = Transaction.transfer(inputs, [user2_vk], input_tx.asset)
+        tx = Transaction.transfer(inputs, [([user2_vk], 1)], input_tx.asset)
         tx = tx.sign([user_sk])
 
         # validate transaction
@@ -776,69 +829,6 @@ class TestMultipleInputs(object):
         assert len(tx.fulfillments) == 1
         assert len(tx.conditions) == 1
 
-    @pytest.mark.skipif(reason=('Multiple inputs are only allowed for the '
-                                'same asset. Remove this after implementing ',
-                                'multiple assets'))
-    @pytest.mark.usefixtures('inputs')
-    def test_transfer_single_owners_multiple_inputs(self, b, user_sk, user_vk):
-        from bigchaindb.common import crypto
-        from bigchaindb.models import Transaction
-
-        user2_sk, user2_vk = crypto.generate_key_pair()
-
-        # get inputs
-        owned_inputs = b.get_owned_ids(user_vk)
-        input_txs = [b.get_transaction(tx_link.txid) for tx_link
-                     in owned_inputs]
-        inputs = sum([input_tx.to_inputs() for input_tx in input_txs], [])
-        tx = Transaction.transfer(inputs, len(inputs) * [[user_vk]])
-        tx = tx.sign([user_sk])
-        assert b.validate_transaction(tx) == tx
-        assert len(tx.fulfillments) == len(inputs)
-        assert len(tx.conditions) == len(inputs)
-
-    @pytest.mark.skipif(reason=('Multiple inputs are only allowed for the '
-                                'same asset. Remove this after implementing ',
-                                'multiple assets'))
-    @pytest.mark.usefixtures('inputs')
-    def test_transfer_single_owners_single_input_from_multiple_outputs(self, b,
-                                                                       user_sk,
-                                                                       user_vk):
-        from bigchaindb.common import crypto
-        from bigchaindb.models import Transaction
-
-        user2_sk, user2_vk = crypto.generate_key_pair()
-
-        # get inputs
-        owned_inputs = b.get_owned_ids(user_vk)
-        input_txs = [b.get_transaction(tx_link.txid) for tx_link
-                     in owned_inputs]
-        inputs = sum([input_tx.to_inputs() for input_tx in input_txs], [])
-        tx = Transaction.transfer(inputs, len(inputs) * [[user2_vk]])
-        tx = tx.sign([user_sk])
-
-        # create block with the transaction
-        block = b.create_block([tx])
-        b.write_block(block, durability='hard')
-
-        # vote block valid
-        vote = b.vote(block.id, b.get_last_voted_block().id, True)
-        b.write_vote(vote)
-
-        # get inputs from user2
-        owned_inputs = b.get_owned_ids(user2_vk)
-        assert len(owned_inputs) == len(inputs)
-
-        # create a transaction with a single input from a multiple output transaction
-        tx_link = owned_inputs.pop()
-        inputs = b.get_transaction(tx_link.txid).to_inputs([0])
-        tx = Transaction.transfer(inputs, [user_vk])
-        tx = tx.sign([user2_sk])
-
-        assert b.is_valid_transaction(tx) == tx
-        assert len(tx.fulfillments) == 1
-        assert len(tx.conditions) == 1
-
     def test_single_owner_before_multiple_owners_after_single_input(self, b,
                                                                     user_sk,
                                                                     user_vk,
@@ -852,47 +842,14 @@ class TestMultipleInputs(object):
         owned_inputs = b.get_owned_ids(user_vk)
         tx_link = owned_inputs.pop()
         input_tx = b.get_transaction(tx_link.txid)
-        tx = Transaction.transfer(input_tx.to_inputs(), [[user2_vk, user3_vk]], input_tx.asset)
+        tx = Transaction.transfer(input_tx.to_inputs(),
+                                  [([user2_vk, user3_vk], 1)], input_tx.asset)
         tx = tx.sign([user_sk])
 
         assert b.is_valid_transaction(tx) == tx
         assert len(tx.fulfillments) == 1
         assert len(tx.conditions) == 1
 
-    @pytest.mark.skipif(reason=('Multiple inputs are only allowed for the '
-                                'same asset. Remove this after implementing ',
-                                'multiple assets'))
-    @pytest.mark.usefixtures('inputs')
-    def test_single_owner_before_multiple_owners_after_multiple_inputs(self, b,
-                                                                       user_sk,
-                                                                       user_vk):
-        from bigchaindb.common import crypto
-        from bigchaindb.models import Transaction
-
-        user2_sk, user2_vk = crypto.generate_key_pair()
-        user3_sk, user3_vk = crypto.generate_key_pair()
-
-        owned_inputs = b.get_owned_ids(user_vk)
-        input_txs = [b.get_transaction(tx_link.txid) for tx_link
-                     in owned_inputs]
-        inputs = sum([input_tx.to_inputs() for input_tx in input_txs], [])
-
-        tx = Transaction.transfer(inputs, len(inputs) * [[user2_vk, user3_vk]])
-        tx = tx.sign([user_sk])
-
-        # create block with the transaction
-        block = b.create_block([tx])
-        b.write_block(block, durability='hard')
-
-        # vote block valid
-        vote = b.vote(block.id, b.get_last_voted_block().id, True)
-        b.write_vote(vote)
-
-        # validate transaction
-        assert b.is_valid_transaction(tx) == tx
-        assert len(tx.fulfillments) == len(inputs)
-        assert len(tx.conditions) == len(inputs)
-
     @pytest.mark.usefixtures('inputs')
     def test_multiple_owners_before_single_owner_after_single_input(self, b,
                                                                     user_sk,
@@ -903,7 +860,7 @@ class TestMultipleInputs(object):
         user2_sk, user2_vk = crypto.generate_key_pair()
         user3_sk, user3_vk = crypto.generate_key_pair()
 
-        tx = Transaction.create([b.me], [user_vk, user2_vk])
+        tx = Transaction.create([b.me], [([user_vk, user2_vk], 1)])
         tx = tx.sign([b.me_private])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -916,7 +873,8 @@ class TestMultipleInputs(object):
         input_tx = b.get_transaction(owned_input.txid)
         inputs = input_tx.to_inputs()
 
-        transfer_tx = Transaction.transfer(inputs, [user3_vk], input_tx.asset)
+        transfer_tx = Transaction.transfer(inputs, [([user3_vk], 1)],
+                                           input_tx.asset)
         transfer_tx = transfer_tx.sign([user_sk, user2_sk])
 
         # validate transaction
@@ -924,29 +882,6 @@ class TestMultipleInputs(object):
         assert len(transfer_tx.fulfillments) == 1
         assert len(transfer_tx.conditions) == 1
 
-    @pytest.mark.skipif(reason=('Multiple inputs are only allowed for the '
-                                'same asset. Remove this after implementing ',
-                                'multiple assets'))
-    @pytest.mark.usefixtures('inputs_shared')
-    def test_multiple_owners_before_single_owner_after_multiple_inputs(self, b,
-                                          user_sk, user_vk, user2_vk, user2_sk):
-        from bigchaindb.common import crypto
-        from bigchaindb.models import Transaction
-
-        # create a new users
-        user3_sk, user3_vk = crypto.generate_key_pair()
-
-        tx_links = b.get_owned_ids(user_vk)
-        inputs = sum([b.get_transaction(tx_link.txid).to_inputs() for tx_link
-                      in tx_links], [])
-
-        tx = Transaction.transfer(inputs, len(inputs) * [[user3_vk]])
-        tx = tx.sign([user_sk, user2_sk])
-
-        assert b.is_valid_transaction(tx) == tx
-        assert len(tx.fulfillments) == len(inputs)
-        assert len(tx.conditions) == len(inputs)
-
     @pytest.mark.usefixtures('inputs')
     def test_multiple_owners_before_multiple_owners_after_single_input(self, b,
                                                                        user_sk,
@@ -958,7 +893,7 @@ class TestMultipleInputs(object):
         user3_sk, user3_vk = crypto.generate_key_pair()
         user4_sk, user4_vk = crypto.generate_key_pair()
 
-        tx = Transaction.create([b.me], [user_vk, user2_vk])
+        tx = Transaction.create([b.me], [([user_vk, user2_vk], 1)])
         tx = tx.sign([b.me_private])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -971,38 +906,14 @@ class TestMultipleInputs(object):
         tx_link = b.get_owned_ids(user_vk).pop()
         tx_input = b.get_transaction(tx_link.txid)
 
-        tx = Transaction.transfer(tx_input.to_inputs(), [[user3_vk, user4_vk]], tx_input.asset)
+        tx = Transaction.transfer(tx_input.to_inputs(),
+                                  [([user3_vk, user4_vk], 1)], tx_input.asset)
         tx = tx.sign([user_sk, user2_sk])
 
         assert b.is_valid_transaction(tx) == tx
         assert len(tx.fulfillments) == 1
         assert len(tx.conditions) == 1
 
-    @pytest.mark.skipif(reason=('Multiple inputs are only allowed for the '
-                                'same asset. Remove this after implementing ',
-                                'multiple assets'))
-    @pytest.mark.usefixtures('inputs_shared')
-    def test_multiple_owners_before_multiple_owners_after_multiple_inputs(self, b,
-                                                                user_sk, user_vk,
-                                                                user2_sk, user2_vk):
-        from bigchaindb.common import crypto
-        from bigchaindb.models import Transaction
-
-        # create a new users
-        user3_sk, user3_vk = crypto.generate_key_pair()
-        user4_sk, user4_vk = crypto.generate_key_pair()
-
-        tx_links = b.get_owned_ids(user_vk)
-        inputs = sum([b.get_transaction(tx_link.txid).to_inputs() for tx_link
-                      in tx_links], [])
-
-        tx = Transaction.transfer(inputs, len(inputs) * [[user3_vk, user4_vk]])
-        tx = tx.sign([user_sk, user2_sk])
-
-        assert b.is_valid_transaction(tx) == tx
-        assert len(tx.fulfillments) == len(inputs)
-        assert len(tx.conditions) == len(inputs)
-
     def test_get_owned_ids_single_tx_single_output(self, b, user_sk, user_vk):
         from bigchaindb.common import crypto
         from bigchaindb.common.transaction import TransactionLink
@@ -1010,7 +921,7 @@ class TestMultipleInputs(object):
 
         user2_sk, user2_vk = crypto.generate_key_pair()
 
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1020,7 +931,7 @@ class TestMultipleInputs(object):
         assert owned_inputs_user1 == [TransactionLink(tx.id, 0)]
         assert owned_inputs_user2 == []
 
-        tx = Transaction.transfer(tx.to_inputs(), [user2_vk], tx.asset)
+        tx = Transaction.transfer(tx.to_inputs(), [([user2_vk], 1)], tx.asset)
         tx = tx.sign([user_sk])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1040,7 +951,7 @@ class TestMultipleInputs(object):
         genesis = b.create_genesis_block()
         user2_sk, user2_vk = crypto.generate_key_pair()
 
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1056,7 +967,8 @@ class TestMultipleInputs(object):
 
         # NOTE: The transaction itself is valid, still will mark the block
         #       as invalid to mock the behavior.
-        tx_invalid = Transaction.transfer(tx.to_inputs(), [user2_vk], tx.asset)
+        tx_invalid = Transaction.transfer(tx.to_inputs(), [([user2_vk], 1)],
+                                          tx.asset)
         tx_invalid = tx_invalid.sign([user_sk])
         block = b.create_block([tx_invalid])
         b.write_block(block, durability='hard')
@@ -1072,47 +984,45 @@ class TestMultipleInputs(object):
         assert owned_inputs_user1 == [TransactionLink(tx.id, 0)]
         assert owned_inputs_user2 == []
 
-    @pytest.mark.skipif(reason=('Multiple inputs are only allowed for the '
-                                'same asset. Remove this after implementing ',
-                                'multiple assets'))
     def test_get_owned_ids_single_tx_multiple_outputs(self, b, user_sk,
                                                       user_vk):
-        import random
         from bigchaindb.common import crypto
-        from bigchaindb.common.transaction import TransactionLink
+        from bigchaindb.common.transaction import TransactionLink, Asset
         from bigchaindb.models import Transaction
 
         user2_sk, user2_vk = crypto.generate_key_pair()
 
-        transactions = []
-        for i in range(2):
-            payload = {'somedata': random.randint(0, 255)}
-            tx = Transaction.create([b.me], [user_vk], payload)
-            tx = tx.sign([b.me_private])
-            transactions.append(tx)
-        block = b.create_block(transactions)
+        # create divisible asset
+        asset = Asset(divisible=True)
+        tx_create = Transaction.create([b.me],
+                                       [([user_vk], 1), ([user_vk], 1)],
+                                       asset=asset)
+        tx_create_signed = tx_create.sign([b.me_private])
+        block = b.create_block([tx_create_signed])
         b.write_block(block, durability='hard')
 
         # get input
         owned_inputs_user1 = b.get_owned_ids(user_vk)
         owned_inputs_user2 = b.get_owned_ids(user2_vk)
 
-        expected_owned_inputs_user1 = [TransactionLink(tx.id, 0) for tx
-                                       in transactions]
+        expected_owned_inputs_user1 = [TransactionLink(tx_create.id, 0),
+                                       TransactionLink(tx_create.id, 1)]
         assert owned_inputs_user1 == expected_owned_inputs_user1
         assert owned_inputs_user2 == []
 
-        inputs = sum([tx.to_inputs() for tx in transactions], [])
-        tx = Transaction.transfer(inputs, len(inputs) * [[user2_vk]])
-        tx = tx.sign([user_sk])
-        block = b.create_block([tx])
+        # transfer divisible asset divided in two outputs
+        tx_transfer = Transaction.transfer(tx_create.to_inputs(),
+                                           [([user2_vk], 1), ([user2_vk], 1)],
+                                           asset=tx_create.asset)
+        tx_transfer_signed = tx_transfer.sign([user_sk])
+        block = b.create_block([tx_transfer_signed])
         b.write_block(block, durability='hard')
 
         owned_inputs_user1 = b.get_owned_ids(user_vk)
         owned_inputs_user2 = b.get_owned_ids(user2_vk)
         assert owned_inputs_user1 == []
-        assert owned_inputs_user2 == [TransactionLink(tx.id, 0),
-                                      TransactionLink(tx.id, 1)]
+        assert owned_inputs_user2 == [TransactionLink(tx_transfer.id, 0),
+                                      TransactionLink(tx_transfer.id, 1)]
 
     def test_get_owned_ids_multiple_owners(self, b, user_sk, user_vk):
         from bigchaindb.common import crypto
@@ -1122,7 +1032,7 @@ class TestMultipleInputs(object):
         user2_sk, user2_vk = crypto.generate_key_pair()
         user3_sk, user3_vk = crypto.generate_key_pair()
 
-        tx = Transaction.create([b.me], [user_vk, user2_vk])
+        tx = Transaction.create([b.me], [([user_vk, user2_vk], 1)])
         tx = tx.sign([b.me_private])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1134,7 +1044,7 @@ class TestMultipleInputs(object):
         assert owned_inputs_user1 == owned_inputs_user2
         assert owned_inputs_user1 == expected_owned_inputs_user1
 
-        tx = Transaction.transfer(tx.to_inputs(), [user3_vk], tx.asset)
+        tx = Transaction.transfer(tx.to_inputs(), [([user3_vk], 1)], tx.asset)
         tx = tx.sign([user_sk, user2_sk])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1150,7 +1060,7 @@ class TestMultipleInputs(object):
 
         user2_sk, user2_vk = crypto.generate_key_pair()
 
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1164,7 +1074,7 @@ class TestMultipleInputs(object):
         assert spent_inputs_user1 is None
 
         # create a transaction and block
-        tx = Transaction.transfer(tx.to_inputs(), [user2_vk], tx.asset)
+        tx = Transaction.transfer(tx.to_inputs(), [([user2_vk], 1)], tx.asset)
         tx = tx.sign([user_sk])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1181,7 +1091,7 @@ class TestMultipleInputs(object):
         # create a new users
         user2_sk, user2_vk = crypto.generate_key_pair()
 
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1199,7 +1109,7 @@ class TestMultipleInputs(object):
         assert spent_inputs_user1 is None
 
         # create a transaction and block
-        tx = Transaction.transfer(tx.to_inputs(), [user2_vk], tx.asset)
+        tx = Transaction.transfer(tx.to_inputs(), [([user2_vk], 1)], tx.asset)
         tx = tx.sign([user_sk])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
@@ -1214,24 +1124,23 @@ class TestMultipleInputs(object):
         # Now there should be no spents (the block is invalid)
         assert spent_inputs_user1 is None
 
-    @pytest.mark.skipif(reason=('Multiple inputs are only allowed for the '
-                                'same asset. Remove this after implementing ',
-                                'multiple assets'))
     def test_get_spent_single_tx_multiple_outputs(self, b, user_sk, user_vk):
-        import random
         from bigchaindb.common import crypto
         from bigchaindb.models import Transaction
+        from bigchaindb.common.transaction import Asset
 
         # create a new users
         user2_sk, user2_vk = crypto.generate_key_pair()
 
-        transactions = []
-        for i in range(3):
-            payload = {'somedata': random.randint(0, 255)}
-            tx = Transaction.create([b.me], [user_vk], payload)
-            tx = tx.sign([b.me_private])
-            transactions.append(tx)
-        block = b.create_block(transactions)
+        # create a divisible asset with 3 outputs
+        asset = Asset(divisible=True)
+        tx_create = Transaction.create([b.me],
+                                       [([user_vk], 1),
+                                        ([user_vk], 1),
+                                        ([user_vk], 1)],
+                                       asset=asset)
+        tx_create_signed = tx_create.sign([b.me_private])
+        block = b.create_block([tx_create_signed])
         b.write_block(block, durability='hard')
 
         owned_inputs_user1 = b.get_owned_ids(user_vk)
@@ -1240,22 +1149,22 @@ class TestMultipleInputs(object):
         for input_tx in owned_inputs_user1:
             assert b.get_spent(input_tx.txid, input_tx.cid) is None
 
-        # select inputs to use
-        inputs = sum([tx.to_inputs() for tx in transactions[:2]], [])
-
-        # create a transaction and block
-        tx = Transaction.transfer(inputs, len(inputs) * [[user2_vk]])
-        tx = tx.sign([user_sk])
-        block = b.create_block([tx])
+        # transfer the first 2 inputs
+        tx_transfer = Transaction.transfer(tx_create.to_inputs()[:2],
+                                           [([user2_vk], 1), ([user2_vk], 1)],
+                                           asset=tx_create.asset)
+        tx_transfer_signed = tx_transfer.sign([user_sk])
+        block = b.create_block([tx_transfer_signed])
         b.write_block(block, durability='hard')
 
         # check that used inputs are marked as spent
-        for ffill in inputs:
-            assert b.get_spent(ffill.tx_input.txid, ffill.tx_input.cid) == tx
+        for ffill in tx_create.to_inputs()[:2]:
+            spent_tx = b.get_spent(ffill.tx_input.txid, ffill.tx_input.cid)
+            assert spent_tx == tx_transfer_signed
 
         # check if remaining transaction that was unspent is also perceived
         # spendable by BigchainDB
-        assert b.get_spent(transactions[2].id, 0) is None
+        assert b.get_spent(tx_create.to_inputs()[2].tx_input.txid, 2) is None
 
     def test_get_spent_multiple_owners(self, b, user_sk, user_vk):
         import random
@@ -1268,7 +1177,8 @@ class TestMultipleInputs(object):
         transactions = []
         for i in range(3):
             payload = {'somedata': random.randint(0, 255)}
-            tx = Transaction.create([b.me], [user_vk, user2_vk], payload)
+            tx = Transaction.create([b.me], [([user_vk, user2_vk], 1)],
+                                    payload)
             tx = tx.sign([b.me_private])
             transactions.append(tx)
         block = b.create_block(transactions)
@@ -1281,7 +1191,8 @@ class TestMultipleInputs(object):
             assert b.get_spent(input_tx.txid, input_tx.cid) is None
 
         # create a transaction
-        tx = Transaction.transfer(transactions[0].to_inputs(), [user3_vk], transactions[0].asset)
+        tx = Transaction.transfer(transactions[0].to_inputs(),
+                                  [([user3_vk], 1)], transactions[0].asset)
         tx = tx.sign([user_sk, user2_sk])
         block = b.create_block([tx])
         b.write_block(block, durability='hard')
diff --git a/tests/pipelines/test_block_creation.py b/tests/pipelines/test_block_creation.py
index c2403a08..171e3ca9 100644
--- a/tests/pipelines/test_block_creation.py
+++ b/tests/pipelines/test_block_creation.py
@@ -45,7 +45,7 @@ def test_create_block(b, user_vk):
     block_maker = BlockPipeline()
 
     for i in range(100):
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         block_maker.create(tx)
 
@@ -63,7 +63,7 @@ def test_write_block(b, user_vk):
 
     txs = []
     for i in range(100):
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         txs.append(tx)
 
@@ -82,7 +82,7 @@ def test_duplicate_transaction(b, user_vk):
 
     txs = []
     for i in range(10):
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         txs.append(tx)
 
@@ -97,8 +97,7 @@ def test_duplicate_transaction(b, user_vk):
     # verify tx is in the backlog
     assert b.connection.run(r.table('backlog').get(txs[0].id)) is not None
 
-    # try to validate a transaction that's already in the chain; should not
-    # work
+    # try to validate a transaction that's already in the chain; should not work
     assert block_maker.validate_tx(txs[0].to_dict()) is None
 
     # duplicate tx should be removed from backlog
@@ -110,7 +109,7 @@ def test_delete_tx(b, user_vk):
     from bigchaindb.pipelines.block import BlockPipeline
     block_maker = BlockPipeline()
     for i in range(100):
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         block_maker.create(tx)
         # make sure the tx appears in the backlog
@@ -139,7 +138,8 @@ def test_prefeed(b, user_vk):
     from bigchaindb.pipelines.block import initial
 
     for i in range(100):
-        tx = Transaction.create([b.me], [user_vk], {'msg': random.random()})
+        tx = Transaction.create([b.me], [([user_vk], 1)],
+                                {'msg': random.random()})
         tx = tx.sign([b.me_private])
         b.write_transaction(tx)
 
@@ -168,7 +168,8 @@ def test_full_pipeline(b, user_vk):
 
     count_assigned_to_me = 0
     for i in range(100):
-        tx = Transaction.create([b.me], [user_vk], {'msg': random.random()})
+        tx = Transaction.create([b.me], [([user_vk], 1)],
+                                {'msg': random.random()})
         tx = tx.sign([b.me_private]).to_dict()
         assignee = random.choice([b.me, 'aaa', 'bbb', 'ccc'])
         tx['assignee'] = assignee
diff --git a/tests/pipelines/test_election.py b/tests/pipelines/test_election.py
index 669a75cb..d62869f5 100644
--- a/tests/pipelines/test_election.py
+++ b/tests/pipelines/test_election.py
@@ -15,7 +15,7 @@ def test_check_for_quorum_invalid(b, user_vk):
     e = election.Election()
 
     # create blocks with transactions
-    tx1 = Transaction.create([b.me], [user_vk])
+    tx1 = Transaction.create([b.me], [([user_vk], 1)])
     test_block = b.create_block([tx1])
 
     # simulate a federation with four voters
@@ -44,7 +44,7 @@ def test_check_for_quorum_invalid_prev_node(b, user_vk):
     e = election.Election()
 
     # create blocks with transactions
-    tx1 = Transaction.create([b.me], [user_vk])
+    tx1 = Transaction.create([b.me], [([user_vk], 1)])
     test_block = b.create_block([tx1])
 
     # simulate a federation with four voters
@@ -74,7 +74,7 @@ def test_check_for_quorum_valid(b, user_vk):
     e = election.Election()
 
     # create blocks with transactions
-    tx1 = Transaction.create([b.me], [user_vk])
+    tx1 = Transaction.create([b.me], [([user_vk], 1)])
     test_block = b.create_block([tx1])
 
     # simulate a federation with four voters
@@ -103,7 +103,7 @@ def test_check_requeue_transaction(b, user_vk):
     e = election.Election()
 
     # create blocks with transactions
-    tx1 = Transaction.create([b.me], [user_vk])
+    tx1 = Transaction.create([b.me], [([user_vk], 1)])
     test_block = b.create_block([tx1])
 
     e.requeue_transactions(test_block)
@@ -131,7 +131,8 @@ def test_full_pipeline(b, user_vk):
     # write two blocks
     txs = []
     for i in range(100):
-        tx = Transaction.create([b.me], [user_vk], {'msg': random.random()})
+        tx = Transaction.create([b.me], [([user_vk], 1)],
+                                {'msg': random.random()})
         tx = tx.sign([b.me_private])
         txs.append(tx)
 
@@ -140,7 +141,8 @@ def test_full_pipeline(b, user_vk):
 
     txs = []
     for i in range(100):
-        tx = Transaction.create([b.me], [user_vk], {'msg': random.random()})
+        tx = Transaction.create([b.me], [([user_vk], 1)],
+                                {'msg': random.random()})
         tx = tx.sign([b.me_private])
         txs.append(tx)
 
diff --git a/tests/pipelines/test_stale_monitor.py b/tests/pipelines/test_stale_monitor.py
index 3a3e6ffe..95f298c5 100644
--- a/tests/pipelines/test_stale_monitor.py
+++ b/tests/pipelines/test_stale_monitor.py
@@ -10,7 +10,7 @@ import os
 
 def test_get_stale(b, user_vk):
     from bigchaindb.models import Transaction
-    tx = Transaction.create([b.me], [user_vk])
+    tx = Transaction.create([b.me], [([user_vk], 1)])
     tx = tx.sign([b.me_private])
     b.write_transaction(tx, durability='hard')
 
@@ -27,7 +27,7 @@ def test_get_stale(b, user_vk):
 def test_reassign_transactions(b, user_vk):
     from bigchaindb.models import Transaction
     # test with single node
-    tx = Transaction.create([b.me], [user_vk])
+    tx = Transaction.create([b.me], [([user_vk], 1)])
     tx = tx.sign([b.me_private])
     b.write_transaction(tx, durability='hard')
 
@@ -36,7 +36,7 @@ def test_reassign_transactions(b, user_vk):
     stm.reassign_transactions(tx.to_dict())
 
     # test with federation
-    tx = Transaction.create([b.me], [user_vk])
+    tx = Transaction.create([b.me], [([user_vk], 1)])
     tx = tx.sign([b.me_private])
     b.write_transaction(tx, durability='hard')
 
@@ -51,7 +51,7 @@ def test_reassign_transactions(b, user_vk):
     assert reassigned_tx['assignee'] != tx['assignee']
 
     # test with node not in federation
-    tx = Transaction.create([b.me], [user_vk])
+    tx = Transaction.create([b.me], [([user_vk], 1)])
     tx = tx.sign([b.me_private]).to_dict()
     tx.update({'assignee': 'lol'})
     tx.update({'assignment_timestamp': time.time()})
@@ -85,7 +85,7 @@ def test_full_pipeline(monkeypatch, user_vk):
     monkeypatch.setattr('time.time', lambda: 1)
 
     for i in range(100):
-        tx = Transaction.create([b.me], [user_vk])
+        tx = Transaction.create([b.me], [([user_vk], 1)])
         tx = tx.sign([b.me_private])
         original_txc.append(tx.to_dict())
 
diff --git a/tests/pipelines/test_vote.py b/tests/pipelines/test_vote.py
index 5bd0eb52..ec2f6204 100644
--- a/tests/pipelines/test_vote.py
+++ b/tests/pipelines/test_vote.py
@@ -8,7 +8,7 @@ from multipipes import Pipe, Pipeline
 
 def dummy_tx(b):
     from bigchaindb.models import Transaction
-    tx = Transaction.create([b.me], [b.me])
+    tx = Transaction.create([b.me], [([b.me], 1)])
     tx = tx.sign([b.me_private])
     return tx
 
@@ -130,7 +130,7 @@ def test_vote_validate_transaction(b):
     assert validation == (True, 123, 1)
 
     # NOTE: Submit unsigned transaction to `validate_tx` yields `False`.
-    tx = Transaction.create([b.me], [b.me])
+    tx = Transaction.create([b.me], [([b.me], 1)])
     validation = vote_obj.validate_tx(tx, 456, 10)
     assert validation == (False, 456, 10)
 
@@ -224,7 +224,7 @@ def test_valid_block_voting_with_create_transaction(b, monkeypatch):
 
     # create a `CREATE` transaction
     test_user_priv, test_user_pub = crypto.generate_key_pair()
-    tx = Transaction.create([b.me], [test_user_pub])
+    tx = Transaction.create([b.me], [([test_user_pub], 1)])
     tx = tx.sign([b.me_private])
 
     monkeypatch.setattr('time.time', lambda: 1)
@@ -265,7 +265,7 @@ def test_valid_block_voting_with_transfer_transactions(monkeypatch, b):
 
     # create a `CREATE` transaction
     test_user_priv, test_user_pub = crypto.generate_key_pair()
-    tx = Transaction.create([b.me], [test_user_pub])
+    tx = Transaction.create([b.me], [([test_user_pub], 1)])
     tx = tx.sign([b.me_private])
 
     monkeypatch.setattr('time.time', lambda: 1)
@@ -274,7 +274,8 @@ def test_valid_block_voting_with_transfer_transactions(monkeypatch, b):
 
     # create a `TRANSFER` transaction
     test_user2_priv, test_user2_pub = crypto.generate_key_pair()
-    tx2 = Transaction.transfer(tx.to_inputs(), [test_user2_pub], tx.asset)
+    tx2 = Transaction.transfer(tx.to_inputs(), [([test_user2_pub], 1)],
+                               tx.asset)
     tx2 = tx2.sign([test_user_priv])
 
     monkeypatch.setattr('time.time', lambda: 2)
@@ -338,7 +339,7 @@ def test_unsigned_tx_in_block_voting(monkeypatch, b, user_vk):
     vote_pipeline.setup(indata=inpipe, outdata=outpipe)
 
     # NOTE: `tx` is invalid, because it wasn't signed.
-    tx = Transaction.create([b.me], [b.me])
+    tx = Transaction.create([b.me], [([b.me], 1)])
     block = b.create_block([tx])
 
     inpipe.put(block.to_dict())
@@ -375,7 +376,7 @@ def test_invalid_id_tx_in_block_voting(monkeypatch, b, user_vk):
     vote_pipeline.setup(indata=inpipe, outdata=outpipe)
 
     # NOTE: `tx` is invalid, because its id is not corresponding to its content
-    tx = Transaction.create([b.me], [b.me])
+    tx = Transaction.create([b.me], [([b.me], 1)])
     tx = tx.sign([b.me_private])
     block = b.create_block([tx]).to_dict()
     block['block']['transactions'][0]['id'] = 'an invalid tx id'
@@ -414,7 +415,7 @@ def test_invalid_content_in_tx_in_block_voting(monkeypatch, b, user_vk):
     vote_pipeline.setup(indata=inpipe, outdata=outpipe)
 
     # NOTE: `tx` is invalid, because its content is not corresponding to its id
-    tx = Transaction.create([b.me], [b.me])
+    tx = Transaction.create([b.me], [([b.me], 1)])
     tx = tx.sign([b.me_private])
     block = b.create_block([tx]).to_dict()
     block['block']['transactions'][0]['id'] = 'an invalid tx id'
diff --git a/tests/test_core.py b/tests/test_core.py
index 84cdba08..55d73e77 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -62,14 +62,13 @@ def test_bigchain_class_initialization_with_parameters(config):
 
 
 def test_get_blocks_status_containing_tx(monkeypatch):
+    from bigchaindb.db.backends.rethinkdb import RethinkDBBackend
     from bigchaindb.core import Bigchain
     blocks = [
         {'id': 1}, {'id': 2}
     ]
-    monkeypatch.setattr(
-        Bigchain, 'search_block_election_on_index', lambda x, y: blocks)
-    monkeypatch.setattr(
-        Bigchain, 'block_election_status', lambda x, y, z: Bigchain.BLOCK_VALID)
+    monkeypatch.setattr(RethinkDBBackend, 'get_blocks_status_from_transaction', lambda x: blocks)
+    monkeypatch.setattr(Bigchain, 'block_election_status', lambda x, y, z: Bigchain.BLOCK_VALID)
     bigchain = Bigchain(public_key='pubkey', private_key='privkey')
     with pytest.raises(Exception):
         bigchain.get_blocks_status_containing_tx('txid')
@@ -85,10 +84,9 @@ def test_has_previous_vote(monkeypatch):
         bigchain.has_previous_vote(block)
 
 
-@pytest.mark.parametrize('items,exists', (((0,), True), ((), False)))
-def test_transaction_exists(monkeypatch, items, exists):
+@pytest.mark.parametrize('count,exists', ((1, True), (0, False)))
+def test_transaction_exists(monkeypatch, count, exists):
     from bigchaindb.core import Bigchain
-    monkeypatch.setattr(
-        RqlQuery, 'run', lambda x, y: namedtuple('response', 'items')(items))
+    monkeypatch.setattr(RqlQuery, 'run', lambda x, y: count)
     bigchain = Bigchain(public_key='pubkey', private_key='privkey')
     assert bigchain.transaction_exists('txid') is exists
diff --git a/tests/test_models.py b/tests/test_models.py
index 5033aebb..534052f9 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -5,7 +5,7 @@ class TestTransactionModel(object):
     def test_validating_an_invalid_transaction(self, b):
         from bigchaindb.models import Transaction
 
-        tx = Transaction.create([b.me], [b.me])
+        tx = Transaction.create([b.me], [([b.me], 1)])
         tx.operation = 'something invalid'
 
         with raises(TypeError):
@@ -41,7 +41,7 @@ class TestBlockModel(object):
         from bigchaindb.common.util import gen_timestamp, serialize
         from bigchaindb.models import Block, Transaction
 
-        transactions = [Transaction.create([b.me], [b.me])]
+        transactions = [Transaction.create([b.me], [([b.me], 1)])]
         timestamp = gen_timestamp()
         voters = ['Qaaa', 'Qbbb']
         expected_block = {
@@ -73,7 +73,7 @@ class TestBlockModel(object):
         from bigchaindb.common.util import gen_timestamp, serialize
         from bigchaindb.models import Block, Transaction
 
-        transactions = [Transaction.create([b.me], [b.me])]
+        transactions = [Transaction.create([b.me], [([b.me], 1)])]
         timestamp = gen_timestamp()
         voters = ['Qaaa', 'Qbbb']
         expected = Block(transactions, b.me, timestamp, voters)
@@ -113,7 +113,7 @@ class TestBlockModel(object):
         from bigchaindb.common.util import gen_timestamp, serialize
         from bigchaindb.models import Block, Transaction
 
-        transactions = [Transaction.create([b.me], [b.me])]
+        transactions = [Transaction.create([b.me], [([b.me], 1)])]
         timestamp = gen_timestamp()
         voters = ['Qaaa', 'Qbbb']
 
@@ -136,7 +136,7 @@ class TestBlockModel(object):
     def test_compare_blocks(self, b):
         from bigchaindb.models import Block, Transaction
 
-        transactions = [Transaction.create([b.me], [b.me])]
+        transactions = [Transaction.create([b.me], [([b.me], 1)])]
 
         assert Block() != 'invalid comparison'
         assert Block(transactions) == Block(transactions)
@@ -146,7 +146,7 @@ class TestBlockModel(object):
         from bigchaindb.common.util import gen_timestamp, serialize
         from bigchaindb.models import Block, Transaction
 
-        transactions = [Transaction.create([b.me], [b.me])]
+        transactions = [Transaction.create([b.me], [([b.me], 1)])]
         timestamp = gen_timestamp()
         voters = ['Qaaa', 'Qbbb']
         expected_block = {
@@ -168,7 +168,7 @@ class TestBlockModel(object):
         from unittest.mock import Mock
         from bigchaindb.models import Transaction
 
-        tx = Transaction.create([b.me], [b.me])
+        tx = Transaction.create([b.me], [([b.me], 1)])
         block = b.create_block([tx])
 
         has_previous_vote = Mock()
diff --git a/tests/web/test_basic_views.py b/tests/web/test_basic_views.py
index 00e40a37..7d382ca5 100644
--- a/tests/web/test_basic_views.py
+++ b/tests/web/test_basic_views.py
@@ -36,7 +36,7 @@ def test_post_create_transaction_endpoint(b, client):
     from bigchaindb.models import Transaction
     user_priv, user_pub = crypto.generate_key_pair()
 
-    tx = Transaction.create([user_pub], [user_pub])
+    tx = Transaction.create([user_pub], [([user_pub], 1)])
     tx = tx.sign([user_priv])
 
     res = client.post(TX_ENDPOINT, data=json.dumps(tx.to_dict()))
@@ -48,7 +48,7 @@ def test_post_create_transaction_with_invalid_id(b, client):
     from bigchaindb.models import Transaction
     user_priv, user_pub = crypto.generate_key_pair()
 
-    tx = Transaction.create([user_pub], [user_pub])
+    tx = Transaction.create([user_pub], [([user_pub], 1)])
     tx = tx.sign([user_priv]).to_dict()
     tx['id'] = 'invalid id'
 
@@ -60,7 +60,7 @@ def test_post_create_transaction_with_invalid_signature(b, client):
     from bigchaindb.models import Transaction
     user_priv, user_pub = crypto.generate_key_pair()
 
-    tx = Transaction.create([user_pub], [user_pub])
+    tx = Transaction.create([user_pub], [([user_pub], 1)])
     tx = tx.sign([user_priv]).to_dict()
     tx['transaction']['fulfillments'][0]['fulfillment'] = 'invalid signature'
 
@@ -77,7 +77,8 @@ def test_post_transfer_transaction_endpoint(b, client, user_vk, user_sk):
 
     input_valid = b.get_owned_ids(user_vk).pop()
     create_tx = b.get_transaction(input_valid.txid)
-    transfer_tx = Transaction.transfer(create_tx.to_inputs(), [user_pub], create_tx.asset)
+    transfer_tx = Transaction.transfer(create_tx.to_inputs(),
+                                       [([user_pub], 1)], create_tx.asset)
     transfer_tx = transfer_tx.sign([user_sk])
 
     res = client.post(TX_ENDPOINT, data=json.dumps(transfer_tx.to_dict()))
@@ -94,7 +95,8 @@ def test_post_invalid_transfer_transaction_returns_400(b, client, user_vk, user_
 
     input_valid = b.get_owned_ids(user_vk).pop()
     create_tx = b.get_transaction(input_valid.txid)
-    transfer_tx = Transaction.transfer(create_tx.to_inputs(), [user_pub], create_tx.asset)
+    transfer_tx = Transaction.transfer(create_tx.to_inputs(),
+                                       [([user_pub], 1)], create_tx.asset)
 
     res = client.post(TX_ENDPOINT, data=json.dumps(transfer_tx.to_dict()))
     assert res.status_code == 400