diff --git a/changelog.d/3725.misc b/changelog.d/3725.misc
new file mode 100644
index 0000000000..91ab9d7137
--- /dev/null
+++ b/changelog.d/3725.misc
@@ -0,0 +1 @@
+The synapse.storage module has been ported to Python 3.
diff --git a/jenkins/prepare_synapse.sh b/jenkins/prepare_synapse.sh
index a30179f2aa..d95ca846c4 100755
--- a/jenkins/prepare_synapse.sh
+++ b/jenkins/prepare_synapse.sh
@@ -31,5 +31,5 @@ $TOX_BIN/pip install 'setuptools>=18.5'
 $TOX_BIN/pip install 'pip>=10'
 
 { python synapse/python_dependencies.py
-  echo lxml psycopg2
+  echo lxml
 } | xargs $TOX_BIN/pip install
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 9c55e79ef5..942d7c721f 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -78,6 +78,9 @@ CONDITIONAL_REQUIREMENTS = {
     "affinity": {
         "affinity": ["affinity"],
     },
+    "postgres": {
+        "psycopg2>=2.6": ["psycopg2"]
+    }
 }
 
 
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 08dffd774f..be61147b9b 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -17,9 +17,10 @@ import sys
 import threading
 import time
 
-from six import iteritems, iterkeys, itervalues
+from six import PY2, iteritems, iterkeys, itervalues
 from six.moves import intern, range
 
+from canonicaljson import json
 from prometheus_client import Histogram
 
 from twisted.internet import defer
@@ -1216,3 +1217,32 @@ class _RollbackButIsFineException(Exception):
     something went wrong.
     """
     pass
+
+
+def db_to_json(db_content):
+    """
+    Take some data from a database row and return a JSON-decoded object.
+
+    Args:
+        db_content (memoryview|buffer|bytes|bytearray|unicode)
+    """
+    # psycopg2 on Python 3 returns memoryview objects, which we need to
+    # cast to bytes to decode
+    if isinstance(db_content, memoryview):
+        db_content = db_content.tobytes()
+
+    # psycopg2 on Python 2 returns buffer objects, which we need to cast to
+    # bytes to decode
+    if PY2 and isinstance(db_content, buffer):
+        db_content = bytes(db_content)
+
+    # Decode it to a Unicode string before feeding it to json.loads, so we
+    # consistenty get a Unicode-containing object out.
+    if isinstance(db_content, (bytes, bytearray)):
+        db_content = db_content.decode('utf8')
+
+    try:
+        return json.loads(db_content)
+    except Exception:
+        logging.warning("Tried to decode '%r' as JSON and failed", db_content)
+        raise
diff --git a/synapse/storage/deviceinbox.py b/synapse/storage/deviceinbox.py
index 73646da025..e06b0bc56d 100644
--- a/synapse/storage/deviceinbox.py
+++ b/synapse/storage/deviceinbox.py
@@ -169,7 +169,7 @@ class DeviceInboxStore(BackgroundUpdateStore):
         local_by_user_then_device = {}
         for user_id, messages_by_device in messages_by_user_then_device.items():
             messages_json_for_user = {}
-            devices = messages_by_device.keys()
+            devices = list(messages_by_device.keys())
             if len(devices) == 1 and devices[0] == "*":
                 # Handle wildcard device_ids.
                 sql = (
diff --git a/synapse/storage/devices.py b/synapse/storage/devices.py
index c0943ecf91..d10ff9e4b9 100644
--- a/synapse/storage/devices.py
+++ b/synapse/storage/devices.py
@@ -24,7 +24,7 @@ from synapse.api.errors import StoreError
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.util.caches.descriptors import cached, cachedInlineCallbacks, cachedList
 
-from ._base import Cache, SQLBaseStore
+from ._base import Cache, SQLBaseStore, db_to_json
 
 logger = logging.getLogger(__name__)
 
@@ -411,7 +411,7 @@ class DeviceStore(SQLBaseStore):
                 if device is not None:
                     key_json = device.get("key_json", None)
                     if key_json:
-                        result["keys"] = json.loads(key_json)
+                        result["keys"] = db_to_json(key_json)
                     device_display_name = device.get("device_display_name", None)
                     if device_display_name:
                         result["device_display_name"] = device_display_name
@@ -466,7 +466,7 @@ class DeviceStore(SQLBaseStore):
             retcol="content",
             desc="_get_cached_user_device",
         )
-        defer.returnValue(json.loads(content))
+        defer.returnValue(db_to_json(content))
 
     @cachedInlineCallbacks()
     def _get_cached_devices_for_user(self, user_id):
@@ -479,7 +479,7 @@ class DeviceStore(SQLBaseStore):
             desc="_get_cached_devices_for_user",
         )
         defer.returnValue({
-            device["device_id"]: json.loads(device["content"])
+            device["device_id"]: db_to_json(device["content"])
             for device in devices
         })
 
@@ -511,7 +511,7 @@ class DeviceStore(SQLBaseStore):
 
                 key_json = device.get("key_json", None)
                 if key_json:
-                    result["keys"] = json.loads(key_json)
+                    result["keys"] = db_to_json(key_json)
                 device_display_name = device.get("device_display_name", None)
                 if device_display_name:
                     result["device_display_name"] = device_display_name
diff --git a/synapse/storage/end_to_end_keys.py b/synapse/storage/end_to_end_keys.py
index 523b4360c3..1f1721e820 100644
--- a/synapse/storage/end_to_end_keys.py
+++ b/synapse/storage/end_to_end_keys.py
@@ -14,13 +14,13 @@
 # limitations under the License.
 from six import iteritems
 
-from canonicaljson import encode_canonical_json, json
+from canonicaljson import encode_canonical_json
 
 from twisted.internet import defer
 
 from synapse.util.caches.descriptors import cached
 
-from ._base import SQLBaseStore
+from ._base import SQLBaseStore, db_to_json
 
 
 class EndToEndKeyStore(SQLBaseStore):
@@ -90,7 +90,7 @@ class EndToEndKeyStore(SQLBaseStore):
 
         for user_id, device_keys in iteritems(results):
             for device_id, device_info in iteritems(device_keys):
-                device_info["keys"] = json.loads(device_info.pop("key_json"))
+                device_info["keys"] = db_to_json(device_info.pop("key_json"))
 
         defer.returnValue(results)
 
diff --git a/synapse/storage/engines/postgres.py b/synapse/storage/engines/postgres.py
index 8a0386c1a4..42225f8a2a 100644
--- a/synapse/storage/engines/postgres.py
+++ b/synapse/storage/engines/postgres.py
@@ -41,13 +41,18 @@ class PostgresEngine(object):
         db_conn.set_isolation_level(
             self.module.extensions.ISOLATION_LEVEL_REPEATABLE_READ
         )
+
+        # Set the bytea output to escape, vs the default of hex
+        cursor = db_conn.cursor()
+        cursor.execute("SET bytea_output TO escape")
+
         # Asynchronous commit, don't wait for the server to call fsync before
         # ending the transaction.
         # https://www.postgresql.org/docs/current/static/wal-async-commit.html
         if not self.synchronous_commit:
-            cursor = db_conn.cursor()
             cursor.execute("SET synchronous_commit TO OFF")
-            cursor.close()
+
+        cursor.close()
 
     def is_deadlock(self, error):
         if isinstance(error, self.module.DatabaseError):
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index f39c8c8461..8bf87f38f7 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -19,7 +19,7 @@ import logging
 from collections import OrderedDict, deque, namedtuple
 from functools import wraps
 
-from six import iteritems
+from six import iteritems, text_type
 from six.moves import range
 
 from canonicaljson import json
@@ -1220,7 +1220,7 @@ class EventsStore(EventFederationStore, EventsWorkerStore, BackgroundUpdateStore
                     "sender": event.sender,
                     "contains_url": (
                         "url" in event.content
-                        and isinstance(event.content["url"], basestring)
+                        and isinstance(event.content["url"], text_type)
                     ),
                 }
                 for event, _ in events_and_contexts
@@ -1529,7 +1529,7 @@ class EventsStore(EventFederationStore, EventsWorkerStore, BackgroundUpdateStore
 
                     contains_url = "url" in content
                     if contains_url:
-                        contains_url &= isinstance(content["url"], basestring)
+                        contains_url &= isinstance(content["url"], text_type)
                 except (KeyError, AttributeError):
                     # If the event is missing a necessary field then
                     # skip over it.
@@ -1910,9 +1910,9 @@ class EventsStore(EventFederationStore, EventsWorkerStore, BackgroundUpdateStore
             (room_id,)
         )
         rows = txn.fetchall()
-        max_depth = max(row[0] for row in rows)
+        max_depth = max(row[1] for row in rows)
 
-        if max_depth <= token.topological:
+        if max_depth < token.topological:
             # We need to ensure we don't delete all the events from the database
             # otherwise we wouldn't be able to send any events (due to not
             # having any backwards extremeties)
diff --git a/synapse/storage/events_worker.py b/synapse/storage/events_worker.py
index 59822178ff..a8326f5296 100644
--- a/synapse/storage/events_worker.py
+++ b/synapse/storage/events_worker.py
@@ -12,6 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+
 import itertools
 import logging
 from collections import namedtuple
@@ -265,7 +266,7 @@ class EventsWorkerStore(SQLBaseStore):
         """
         with Measure(self._clock, "_fetch_event_list"):
             try:
-                event_id_lists = zip(*event_list)[0]
+                event_id_lists = list(zip(*event_list))[0]
                 event_ids = [
                     item for sublist in event_id_lists for item in sublist
                 ]
@@ -299,14 +300,14 @@ class EventsWorkerStore(SQLBaseStore):
                 logger.exception("do_fetch")
 
                 # We only want to resolve deferreds from the main thread
-                def fire(evs):
+                def fire(evs, exc):
                     for _, d in evs:
                         if not d.called:
                             with PreserveLoggingContext():
-                                d.errback(e)
+                                d.errback(exc)
 
                 with PreserveLoggingContext():
-                    self.hs.get_reactor().callFromThread(fire, event_list)
+                    self.hs.get_reactor().callFromThread(fire, event_list, e)
 
     @defer.inlineCallbacks
     def _enqueue_events(self, events, check_redacted=True, allow_rejected=False):
diff --git a/synapse/storage/filtering.py b/synapse/storage/filtering.py
index 2d5896c5b4..6ddcc909bf 100644
--- a/synapse/storage/filtering.py
+++ b/synapse/storage/filtering.py
@@ -13,14 +13,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from canonicaljson import encode_canonical_json, json
+from canonicaljson import encode_canonical_json
 
 from twisted.internet import defer
 
 from synapse.api.errors import Codes, SynapseError
 from synapse.util.caches.descriptors import cachedInlineCallbacks
 
-from ._base import SQLBaseStore
+from ._base import SQLBaseStore, db_to_json
 
 
 class FilteringStore(SQLBaseStore):
@@ -44,7 +44,7 @@ class FilteringStore(SQLBaseStore):
             desc="get_user_filter",
         )
 
-        defer.returnValue(json.loads(bytes(def_json).decode("utf-8")))
+        defer.returnValue(db_to_json(def_json))
 
     def add_user_filter(self, user_localpart, user_filter):
         def_json = encode_canonical_json(user_filter)
diff --git a/synapse/storage/pusher.py b/synapse/storage/pusher.py
index 8443bd4c1b..c7987bfcdd 100644
--- a/synapse/storage/pusher.py
+++ b/synapse/storage/pusher.py
@@ -15,7 +15,8 @@
 # limitations under the License.
 
 import logging
-import types
+
+import six
 
 from canonicaljson import encode_canonical_json, json
 
@@ -27,6 +28,11 @@ from ._base import SQLBaseStore
 
 logger = logging.getLogger(__name__)
 
+if six.PY2:
+    db_binary_type = buffer
+else:
+    db_binary_type = memoryview
+
 
 class PusherWorkerStore(SQLBaseStore):
     def _decode_pushers_rows(self, rows):
@@ -34,18 +40,18 @@ class PusherWorkerStore(SQLBaseStore):
             dataJson = r['data']
             r['data'] = None
             try:
-                if isinstance(dataJson, types.BufferType):
+                if isinstance(dataJson, db_binary_type):
                     dataJson = str(dataJson).decode("UTF8")
 
                 r['data'] = json.loads(dataJson)
             except Exception as e:
                 logger.warn(
                     "Invalid JSON in data for pusher %d: %s, %s",
-                    r['id'], dataJson, e.message,
+                    r['id'], dataJson, e.args[0],
                 )
                 pass
 
-            if isinstance(r['pushkey'], types.BufferType):
+            if isinstance(r['pushkey'], db_binary_type):
                 r['pushkey'] = str(r['pushkey']).decode("UTF8")
 
         return rows
diff --git a/synapse/storage/transactions.py b/synapse/storage/transactions.py
index 428e7fa36e..0c42bd3322 100644
--- a/synapse/storage/transactions.py
+++ b/synapse/storage/transactions.py
@@ -18,14 +18,14 @@ from collections import namedtuple
 
 import six
 
-from canonicaljson import encode_canonical_json, json
+from canonicaljson import encode_canonical_json
 
 from twisted.internet import defer
 
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.util.caches.descriptors import cached
 
-from ._base import SQLBaseStore
+from ._base import SQLBaseStore, db_to_json
 
 # py2 sqlite has buffer hardcoded as only binary type, so we must use it,
 # despite being deprecated and removed in favor of memoryview
@@ -95,7 +95,8 @@ class TransactionStore(SQLBaseStore):
         )
 
         if result and result["response_code"]:
-            return result["response_code"], json.loads(str(result["response_json"]))
+            return result["response_code"], db_to_json(result["response_json"])
+
         else:
             return None
 
diff --git a/tests/rest/client/v1/utils.py b/tests/rest/client/v1/utils.py
index 40dc4ea256..530dc8ba6d 100644
--- a/tests/rest/client/v1/utils.py
+++ b/tests/rest/client/v1/utils.py
@@ -240,7 +240,6 @@ class RestHelper(object):
         self.assertEquals(200, code)
         defer.returnValue(response)
 
-    @defer.inlineCallbacks
     def send(self, room_id, body=None, txn_id=None, tok=None, expect_code=200):
         if txn_id is None:
             txn_id = "m%s" % (str(time.time()))
@@ -248,9 +247,16 @@ class RestHelper(object):
             body = "body_text_here"
 
         path = "/_matrix/client/r0/rooms/%s/send/m.room.message/%s" % (room_id, txn_id)
-        content = '{"msgtype":"m.text","body":"%s"}' % body
+        content = {"msgtype": "m.text", "body": body}
         if tok:
             path = path + "?access_token=%s" % tok
 
-        (code, response) = yield self.mock_resource.trigger("PUT", path, content)
-        self.assertEquals(expect_code, code, msg=str(response))
+        request, channel = make_request("PUT", path, json.dumps(content).encode('utf8'))
+        render(request, self.resource, self.hs.get_reactor())
+
+        assert int(channel.result["code"]) == expect_code, (
+            "Expected: %d, got: %d, resp: %r"
+            % (expect_code, int(channel.result["code"]), channel.result["body"])
+        )
+
+        return channel.json_body
diff --git a/tests/storage/test_purge.py b/tests/storage/test_purge.py
new file mode 100644
index 0000000000..f671599cb8
--- /dev/null
+++ b/tests/storage/test_purge.py
@@ -0,0 +1,106 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.rest.client.v1 import room
+
+from tests.unittest import HomeserverTestCase
+
+
+class PurgeTests(HomeserverTestCase):
+
+    user_id = "@red:server"
+    servlets = [room.register_servlets]
+
+    def make_homeserver(self, reactor, clock):
+        hs = self.setup_test_homeserver("server", http_client=None)
+        return hs
+
+    def prepare(self, reactor, clock, hs):
+        self.room_id = self.helper.create_room_as(self.user_id)
+
+    def test_purge(self):
+        """
+        Purging a room will delete everything before the topological point.
+        """
+        # Send four messages to the room
+        first = self.helper.send(self.room_id, body="test1")
+        second = self.helper.send(self.room_id, body="test2")
+        third = self.helper.send(self.room_id, body="test3")
+        last = self.helper.send(self.room_id, body="test4")
+
+        storage = self.hs.get_datastore()
+
+        # Get the topological token
+        event = storage.get_topological_token_for_event(last["event_id"])
+        self.pump()
+        event = self.successResultOf(event)
+
+        # Purge everything before this topological token
+        purge = storage.purge_history(self.room_id, event, True)
+        self.pump()
+        self.assertEqual(self.successResultOf(purge), None)
+
+        # Try and get the events
+        get_first = storage.get_event(first["event_id"])
+        get_second = storage.get_event(second["event_id"])
+        get_third = storage.get_event(third["event_id"])
+        get_last = storage.get_event(last["event_id"])
+        self.pump()
+
+        # 1-3 should fail and last will succeed, meaning that 1-3 are deleted
+        # and last is not.
+        self.failureResultOf(get_first)
+        self.failureResultOf(get_second)
+        self.failureResultOf(get_third)
+        self.successResultOf(get_last)
+
+    def test_purge_wont_delete_extrems(self):
+        """
+        Purging a room will delete everything before the topological point.
+        """
+        # Send four messages to the room
+        first = self.helper.send(self.room_id, body="test1")
+        second = self.helper.send(self.room_id, body="test2")
+        third = self.helper.send(self.room_id, body="test3")
+        last = self.helper.send(self.room_id, body="test4")
+
+        storage = self.hs.get_datastore()
+
+        # Set the topological token higher than it should be
+        event = storage.get_topological_token_for_event(last["event_id"])
+        self.pump()
+        event = self.successResultOf(event)
+        event = "t{}-{}".format(
+            *list(map(lambda x: x + 1, map(int, event[1:].split("-"))))
+        )
+
+        # Purge everything before this topological token
+        purge = storage.purge_history(self.room_id, event, True)
+        self.pump()
+        f = self.failureResultOf(purge)
+        self.assertIn("greater than forward", f.value.args[0])
+
+        # Try and get the events
+        get_first = storage.get_event(first["event_id"])
+        get_second = storage.get_event(second["event_id"])
+        get_third = storage.get_event(third["event_id"])
+        get_last = storage.get_event(last["event_id"])
+        self.pump()
+
+        # Nothing is deleted.
+        self.successResultOf(get_first)
+        self.successResultOf(get_second)
+        self.successResultOf(get_third)
+        self.successResultOf(get_last)
diff --git a/tests/unittest.py b/tests/unittest.py
index d852e2465a..8b513bb32b 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -151,6 +151,7 @@ class HomeserverTestCase(TestCase):
         hijack_auth (bool): Whether to hijack auth to return the user specified
         in user_id.
     """
+
     servlets = []
     hijack_auth = True
 
@@ -279,3 +280,13 @@ class HomeserverTestCase(TestCase):
         kwargs = dict(kwargs)
         kwargs.update(self._hs_args)
         return setup_test_homeserver(self.addCleanup, *args, **kwargs)
+
+    def pump(self):
+        """
+        Pump the reactor enough that Deferreds will fire.
+        """
+        self.reactor.pump([0.0] * 100)
+
+    def get_success(self, d):
+        self.pump()
+        return self.successResultOf(d)
diff --git a/tests/utils.py b/tests/utils.py
index 657c258a6e..179b592501 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -147,6 +147,8 @@ def setup_test_homeserver(
         config.max_mau_value = 50
         config.mau_limits_reserved_threepids = []
         config.admin_contact = None
+        config.rc_messages_per_second = 10000
+        config.rc_message_burst_count = 10000
 
         # we need a sane default_room_version, otherwise attempts to create rooms will
         # fail.