diff --git a/developer_manual/externalapi.rst b/developer_manual/externalapi.rst
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@@ -0,0 +1,42 @@
+External API
+============
+
+.. sectionauthor:: Tom Needham <tom@owncloud.com>
+
+Introduction
+------------
+The external API inside ownCloud allows third party developers to access data provided by ownCloud apps. ownCloud version 5.0 will follow the OCS V1.7 specification `found here (draft) <http://www.freedesktop.org/wiki/Specifications/open-collaboration-services-1.7>`_.
+
+Usage
+------------
+To make use of the external api as an app developer, there are just three things to do.
+
+#. Add your API routes inside $app/appinfo/routes.php
+#. Code your API methods in $app/lib/*
+#. Update the OCS spec with your call
+
+To register your API routes, we make use of the OCP\API::register() method as defined below:
+
+.. php:class:: OCP\\API
+
+  OCP\\API class
+
+  .. php:method:: register($method, $url, $action, $app, $authlevel, $defaults, $requirements)
+
+      Registers an API route with the backend.
+
+      :param string $method: The HTTP method (get, post, put or delete)
+      :param string $url: The url that defines the API route (see 'Routing URLs' section below)
+      :param callable $action: The function to call
+      :param string $app: The app id
+      :param int $authlevel: The required level of authentication to access the API method (use constants `defined in OC_API <https://github.com/owncloud/core/blob/ocs_api/lib/api.php#L32>`_)
+      :param array $defaults: associative array of defaults for the URL parameters. Keys are the parameter names as defined in the url
+      :param array $requirements: associative array of requirements for the url parameters (See the `Symfony Documentation <http://symfony.com/doc/2.0/book/routing.html#adding-requirements>`_)
+      
+Routing URLs
+~~~~~~~~~~~~~
+The API uses the new routing features inside ownCloud to make it easy to attach api methods to urls which include variables. To register an API method including a variable, simple place the variable name in curly brackets {}. For example:
+
+   /cloud/users/{userid}
+
+If the URL /cloud/users/Tom is requested, the api function registered with this url would be called, and passed the parameter 'userid' with the value: 'Tom'. The parameters are passed to the API methods inside an array.
\ No newline at end of file
diff --git a/developer_manual/index.rst b/developer_manual/index.rst
index 12f71c08e..52120ad43 100644
--- a/developer_manual/index.rst
+++ b/developer_manual/index.rst
@@ -18,6 +18,7 @@ Contents
    vcategories
    routing
    apps
+   externalapi