diff --git a/lib/group.php b/lib/group.php
index ceee5fa4edb787f0a0217ca8e69591b5078265b6..12e5f5ebb30ff82cccc343b456fec5232d6425cf 100644
--- a/lib/group.php
+++ b/lib/group.php
@@ -43,7 +43,7 @@ class OC_Group {
 	 * @returns true/false
 	 */
 	public static function useBackend( $backend ){
-		if($backend instanceof OC_Group_Backend){
+		if($backend instanceof OC_Group_Interface){
 			self::$_usedBackends[]=$backend;
 		}
 	}
@@ -168,7 +168,7 @@ class OC_Group {
 
 		if($run){
 			$succes=false;
-			
+
 			//add the user to the all backends that have the group
 			foreach(self::$_usedBackends as $backend){
 				if(!$backend->implementsActions(OC_GROUP_BACKEND_ADD_TO_GROUP))
@@ -245,7 +245,7 @@ class OC_Group {
 		asort($groups);
 		return $groups;
 	}
-	
+
 	/**
 	 * check if a group exists
 	 * @param string $gid
@@ -259,7 +259,7 @@ class OC_Group {
 		}
 		return false;
 	}
-	
+
 	/**
 	 * @brief get a list of all users in a group
 	 * @returns array with user ids
diff --git a/lib/group/backend.php b/lib/group/backend.php
index 24778afd1e56c3859684f7fb635abf5d22b964c7..ebc078f152a85d850e3597862b3289c6bc7ad240 100644
--- a/lib/group/backend.php
+++ b/lib/group/backend.php
@@ -37,7 +37,7 @@ define('OC_GROUP_BACKEND_REMOVE_FROM_GOUP',  0x00001000);
 /**
  * Abstract base class for user management
  */
-abstract class OC_Group_Backend {
+abstract class OC_Group_Backend implements OC_Group_Interface {
 	protected $possibleActions = array(
 		OC_GROUP_BACKEND_CREATE_GROUP => 'createGroup',
 		OC_GROUP_BACKEND_DELETE_GROUP => 'deleteGroup',
diff --git a/lib/group/interface.php b/lib/group/interface.php
new file mode 100644
index 0000000000000000000000000000000000000000..f86a6dd0898b6a7e383c6017c1cb5fb94f7a617f
--- /dev/null
+++ b/lib/group/interface.php
@@ -0,0 +1,86 @@
+<?php
+
+/**
+ * ownCloud - group interface
+ *
+ * @author Arthur Schiwon
+ * @copyright 2012 Arthur Schiwon blizzz@owncloud.org
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU AFFERO GENERAL PUBLIC LICENSE for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+interface OC_Group_Interface {
+
+	/**
+	* @brief Get all supported actions
+	* @returns bitwise-or'ed actions
+	*
+	* Returns the supported actions as int to be
+	* compared with OC_USER_BACKEND_CREATE_USER etc.
+	*/
+	public function getSupportedActions();
+
+	/**
+	* @brief Check if backend implements actions
+	* @param $actions bitwise-or'ed actions
+	* @returns boolean
+	*
+	* Returns the supported actions as int to be
+	* compared with OC_GROUP_BACKEND_CREATE_GROUP etc.
+	*/
+	public function implementsActions($actions);
+
+	/**
+	 * @brief is user in group?
+	 * @param $uid uid of the user
+	 * @param $gid gid of the group
+	 * @returns true/false
+	 *
+	 * Checks whether the user is member of a group or not.
+	 */
+	public function inGroup($uid, $gid);
+
+	/**
+	 * @brief Get all groups a user belongs to
+	 * @param $uid Name of the user
+	 * @returns array with group names
+	 *
+	 * This function fetches all groups a user belongs to. It does not check
+	 * if the user exists at all.
+	 */
+	public function getUserGroups($uid);
+
+	/**
+	 * @brief get a list of all groups
+	 * @returns array with group names
+	 *
+	 * Returns a list with all groups
+	 */
+	public function getGroups();
+
+	/**
+	 * check if a group exists
+	 * @param string $gid
+	 * @return bool
+	 */
+	public function groupExists($gid);
+
+	/**
+	 * @brief get a list of all users in a group
+	 * @returns array with user ids
+	 */
+	public function usersInGroup($gid);
+
+}
\ No newline at end of file