diff --git a/son_manipulator.py b/son_manipulator.py
new file mode 100644
index 000000000..f5f3aa6c1
--- /dev/null
+++ b/son_manipulator.py
@@ -0,0 +1,58 @@
+"""Manipulators that can edit SON objects as the enter and exit a database.
+
+New manipulators should be defined as subclasses of SONManipulator and can be
+installed on a database by calling `Database.add_son_manipulator`."""
+
+from objectid import ObjectId
+
+class SONManipulator(object):
+    """A base son manipulator.
+
+    This manipulator just saves and restores objects without changing them.
+    """
+    def __init__(self, database):
+        """Instantiate the manager.
+
+        Arguments:
+        - `database`: a Mongo Database
+        """
+        self.__database = database
+
+    def transform_incoming(self, son, collection):
+        """Manipulate an incoming son object.
+
+        Arguments:
+        - `son`: the son object to be inserted into the database
+        - `collection`: the collection the object is being inserted into
+        """
+        return son
+
+    def transform_outgoing(self, son, collection):
+        """Manipulate an outgoing son object.
+
+        Arguments:
+        - `son`: the son object being retrieved from the database
+        - `collection`: the collection this object was stored in
+        """
+        return son
+
+class ObjectIdInjector(SONManipulator):
+    """A son manipulator that adds the _id field if it is missing.
+    """
+    def transform_incoming(self, son, collection):
+        """Add an _id field if it is missing.
+        """
+        if "_id" in son:
+            assert isinstance(son["_id"], ObjectId), "'_id' must be an ObjectId"
+        else:
+            son["_id"] = ObjectId()
+        return son
+
+class NamespaceInjector(SONManipulator):
+    """A son manipulator that adds the _ns field.
+    """
+    def transform_incoming(self, son, collection):
+        """Add the _ns field to the incoming object
+        """
+        son["_ns"] = collection.name()
+        return son
diff --git a/test/test_son_manipulator.py b/test/test_son_manipulator.py
new file mode 100644
index 000000000..524ff2557
--- /dev/null
+++ b/test/test_son_manipulator.py
@@ -0,0 +1,64 @@
+"""Tests for SONManipulators.
+"""
+
+import unittest
+
+import qcheck
+from objectid import ObjectId
+from son_manipulator import SONManipulator, ObjectIdInjector, NamespaceInjector
+from database import Database
+from test_connection import get_connection
+
+class TestSONManipulator(unittest.TestCase):
+    def setUp(self):
+        self.db = Database(get_connection(), "test")
+
+    def test_basic(self):
+        manip = SONManipulator(self.db)
+        collection = self.db.test
+
+        def incoming_is_identity(son):
+            return son == manip.transform_incoming(son, collection)
+        qcheck.check_unittest(self, incoming_is_identity,
+                              qcheck.gen_mongo_dict(3))
+
+        def outgoing_is_identity(son):
+            return son == manip.transform_outgoing(son, collection)
+        qcheck.check_unittest(self, outgoing_is_identity,
+                              qcheck.gen_mongo_dict(3))
+
+    def test_id_injection(self):
+        manip = ObjectIdInjector(self.db)
+        collection = self.db.test
+
+        def incoming_adds_id(son):
+            son = manip.transform_incoming(son, collection)
+            assert "_id" in son
+            assert isinstance(son["_id"], ObjectId)
+            return True
+        qcheck.check_unittest(self, incoming_adds_id,
+                              qcheck.gen_mongo_dict(3))
+
+        def outgoing_is_identity(son):
+            return son == manip.transform_outgoing(son, collection)
+        qcheck.check_unittest(self, outgoing_is_identity,
+                              qcheck.gen_mongo_dict(3))
+
+    def test_ns_injection(self):
+        manip = NamespaceInjector(self.db)
+        collection = self.db.test
+
+        def incoming_adds_ns(son):
+            son = manip.transform_incoming(son, collection)
+            assert "_ns" in son
+            return son["_ns"] == collection.name()
+        qcheck.check_unittest(self, incoming_adds_ns,
+                              qcheck.gen_mongo_dict(3))
+
+        def outgoing_is_identity(son):
+            return son == manip.transform_outgoing(son, collection)
+        qcheck.check_unittest(self, outgoing_is_identity,
+                              qcheck.gen_mongo_dict(3))
+
+if __name__ == "__main__":
+    unittest.main()