diff --git a/gcloud/datastore/__init__.py b/gcloud/datastore/__init__.py
index 0a9c515a5ed8b..2972fa4f835e3 100644
--- a/gcloud/datastore/__init__.py
+++ b/gcloud/datastore/__init__.py
@@ -84,6 +84,9 @@ def set_default_dataset_id(dataset_id=None):
     if dataset_id is None:
         dataset_id = os.getenv(_DATASET_ENV_VAR_NAME)
 
+    if dataset_id is None:
+        dataset_id = _implicit_environ.app_engine_id()
+
     if dataset_id is not None:
         _implicit_environ.DATASET_ID = dataset_id
 
diff --git a/gcloud/datastore/_implicit_environ.py b/gcloud/datastore/_implicit_environ.py
index 8410ab7cdece6..f210270ac71da 100644
--- a/gcloud/datastore/_implicit_environ.py
+++ b/gcloud/datastore/_implicit_environ.py
@@ -4,9 +4,27 @@
 imply the current dataset ID and connection from the enviroment.
 """
 
+try:
+    from google.appengine.api import app_identity
+except ImportError:
+    app_identity = None
+
 
 DATASET_ID = None
 """Module global to allow persistent implied dataset ID from enviroment."""
 
 CONNECTION = None
 """Module global to allow persistent implied connection from enviroment."""
+
+
+def app_engine_id():
+    """Gets the App Engine application ID if it can be found.
+
+    :rtype: string or ``NoneType``
+    :returns: App Engine application ID if running in App Engine,
+              else ``None``.
+    """
+    if app_identity is None:
+        return None
+
+    return app_identity.get_application_id()
diff --git a/gcloud/datastore/test___init__.py b/gcloud/datastore/test___init__.py
index 7c836b1d7c0ac..9d484c85f63bd 100644
--- a/gcloud/datastore/test___init__.py
+++ b/gcloud/datastore/test___init__.py
@@ -78,6 +78,33 @@ def test_set_explicit_None_w_env_var_set(self):
             self._callFUT(None)
         self.assertEqual(_implicit_environ.DATASET_ID, IMPLICIT_DATASET_ID)
 
+    def test_set_implicit_from_appengine(self):
+        from gcloud._testing import _Monkey
+        from gcloud.datastore import _implicit_environ
+
+        APP_ENGINE_ID = 'GAE'
+        APP_IDENTITY = _AppIdentity(APP_ENGINE_ID)
+
+        with self._monkey(None):
+            with _Monkey(_implicit_environ, app_identity=APP_IDENTITY):
+                self._callFUT()
+
+        self.assertEqual(_implicit_environ.DATASET_ID, APP_ENGINE_ID)
+
+    def test_set_implicit_both_env_and_appengine(self):
+        from gcloud._testing import _Monkey
+        from gcloud.datastore import _implicit_environ
+
+        IMPLICIT_DATASET_ID = 'IMPLICIT'
+        APP_ENGINE_ID = 'GAE'
+        APP_IDENTITY = _AppIdentity(APP_ENGINE_ID)
+
+        with self._monkey(IMPLICIT_DATASET_ID):
+            with _Monkey(_implicit_environ, app_identity=APP_IDENTITY):
+                self._callFUT()
+
+        self.assertEqual(_implicit_environ.DATASET_ID, IMPLICIT_DATASET_ID)
+
 
 class Test_set_default_connection(unittest2.TestCase):
 
@@ -165,3 +192,12 @@ def test_it(self):
         self.assertTrue(isinstance(found, Connection))
         self.assertTrue(found._credentials is client._signed)
         self.assertTrue(client._get_app_default_called)
+
+
+class _AppIdentity(object):
+
+    def __init__(self, app_id):
+        self.app_id = app_id
+
+    def get_application_id(self):
+        return self.app_id