diff --git a/doc/source/index.rst b/doc/source/index.rst
index f693c25ff039..a9e42cc92b91 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -97,6 +97,7 @@ APIs Development
    api_plugins
    api_microversion_dev
    policy_enforcement
+   stable_api
 
 Concepts
 ---------
diff --git a/doc/source/stable_api.rst b/doc/source/stable_api.rst
new file mode 100644
index 000000000000..22145f7e7011
--- /dev/null
+++ b/doc/source/stable_api.rst
@@ -0,0 +1,92 @@
+..
+      Copyright 2015 Intel
+      All Rights Reserved.
+
+      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.
+
+
+Nova Stable REST API
+====================
+
+This document describes both the current state of the Nova REST API -- as
+of the Kilo release -- and also attempts to describe how the Nova team intends
+to evolve the REST API's implementation over time and remove some of the
+cruft that has crept in over the years.
+
+Background
+----------
+
+Nova currently includes two distinct frameworks for exposing REST API
+functionality. Older code is called the "V2 API" and exists in the
+/nova/api/openstack/compute/contrib/ directory. Newer code is called the
+"v2.1 API" and exists in the /nova/api/openstack/compute/plugins directory.
+
+The V2 API is the old Nova REST API. It will be replaced by V2.1 API totally.
+The code tree of V2 API will be removed in the future also.
+
+The V2.1 API is the new Nova REST API with a set of improvements which
+includes Mircoversion and standardized validation of inputs using JSON-Schema.
+Also the V2.1 API is totally backwards compatible with the V2 API (That is the
+reason we call it as V2.1 API).
+
+Stable API
+----------
+
+In the V2 API, there is a concept called 'extension'. An operator can use it
+to enable/disable part of Nova REST API based on requirements. And end user
+may query the '/extensions' API to discover what *API functionality* is
+supported by the Nova deployment.
+
+Unfortunately, because V2 API extensions could be enabled or disabled
+from one deployment to another -- as well as custom API extensions added
+to one deployment and not another -- it was impossible for an end user to
+know what the OpenStack Compute API actually included. No two OpenStack
+deployments were consistent, which made cloud interoperability impossible.
+
+API extensions, while not (yet) removed from the V2.1 API, are no longer
+needed to evolve the REST API, and no new API functionality should use
+the API extension classes to implement new functionality. Instead, new
+API functionality should use the microversioning decorators to add or change
+the REST API.
+
+The extension is considered as two things in the Nova V2.1 API:
+
+* The '/extensions' API
+
+  In the V2 API the user can query it to determine what APIs are supported by
+  the current Nova deployment.
+
+  In V2.1 API, microversions enable us to add new features in backwards-
+  compatible ways. And microversions not only enable us to add new futures by
+  backwards-compatible method, also can be added by appropriate backwards-
+  incompatible method.
+
+  The '/extensions' API is frozen in Nova V2.1 API and will be deprecated
+  in the future.
+
+* The plugin framework
+
+  One of the improvements in the V2.1 API was using stevedore to load
+  Nova REST API extensions instead of old V2 handcrafted extension load
+  mechanisim.
+
+  There was an argument that the plugin framework supported extensibility in
+  the Nova API to allow deployers to publish custom API resources.
+
+  We will keep the existing plugin mechanisms in place within Nova but only
+  to enable modularity in the codebase, not to allow extending of the Nova
+  REST API.
+
+As the extension will be removed from Nove V2.1 REST API. So the concept of
+core API and extension API is eliminated also. There is no difference between
+Nova V2.1 REST API, all of them are part of Nova stable REST API.