diff --git a/objectid.py b/objectid.py
new file mode 100644
index 000000000..e17d94ce7
--- /dev/null
+++ b/objectid.py
@@ -0,0 +1,100 @@
+"""Representation of an ObjectId for Mongo."""
+
+import random
+import types
+import unittest
+
+class InvalidId(ValueError):
+    """Raised when trying to create an ObjectId from invalid data.
+    """
+
+class ObjectId(object):
+    """A Mongo ObjectId.
+    """
+    def __init__(self, id=None):
+        """Initialize a new ObjectId.
+
+        If no value of id is given, create a new (unique) ObjectId. If given id
+        is an instance of (string, ObjectId) validate it and use that.
+        Otherwise, a TypeError is raised. If given an invalid id, InvalidId is
+        raised.
+
+        Arguments:
+        - `id` (optional): a valid ObjectId
+        """
+        if id == None:
+            self.__generate()
+        else:
+            self.__validate(id)
+
+    def __generate(self):
+        """Generate a new value for this ObjectId.
+        """
+        # TODO for now, just generate 12 random bytes. this will change when we decide on an _id algorithm...
+        id = ""
+        for _ in range(12):
+            id += chr(random.randint(0, 255))
+
+        self.__id = id
+
+    def __validate(self, id):
+        """Validate and use the given id for this ObjectId.
+
+        Raises TypeError if id is not an instance of (str, ObjectId) and
+        InvalidId if it is not a valid ObjectId.
+
+        Arguments:
+        - `id`: a valid ObjectId
+        """
+        if isinstance(id, ObjectId):
+            self.__id = id.__id
+        elif isinstance(id, types.StringType):
+            if len(id) == 12:
+                self.__id = id
+            else:
+                raise InvalidId("%s is not a valid ObjectId" % id)
+        else:
+            raise TypeError("id must be an instance of (str, ObjectId), not %s" % type(id))
+
+    def __str__(self):
+        return self.__id
+
+    def __repr__(self):
+        return "ObjectId('%s')" % self.__id
+
+    def __cmp__(self, other):
+        if isinstance(other, ObjectId):
+            return cmp(self.__id, other.__id)
+        return NotImplemented
+
+class TestObjectId(unittest.TestCase):
+    def setUp(self):
+        pass
+
+    def test_creation(self):
+        self.assertRaises(TypeError, ObjectId, 4)
+        self.assertRaises(TypeError, ObjectId, u"hello")
+        self.assertRaises(TypeError, ObjectId, 175.0)
+        self.assertRaises(TypeError, ObjectId, {"test": 4})
+        self.assertRaises(TypeError, ObjectId, ["something"])
+        self.assertRaises(InvalidId, ObjectId, "")
+        self.assertRaises(InvalidId, ObjectId, "12345678901")
+        self.assertRaises(InvalidId, ObjectId, "1234567890123")
+        self.assertTrue(ObjectId())
+        self.assertTrue(ObjectId("123456789012"))
+        a = ObjectId()
+        self.assertTrue(ObjectId(a))
+
+    def test_repr_str(self):
+        self.assertEqual(repr(ObjectId("123456789012")), "ObjectId('123456789012')")
+        self.assertEqual(str(ObjectId("123456789012")), "123456789012")
+
+    def test_cmp(self):
+        a = ObjectId()
+        self.assertEqual(a, ObjectId(a))
+        self.assertEqual(ObjectId("123456789012"), ObjectId("123456789012"))
+        self.assertNotEqual(ObjectId(), ObjectId())
+        self.assertNotEqual(ObjectId("123456789012"), "123456789012")
+
+if __name__ == "__main__":
+    unittest.main()