The German Literature Archive Marbach, the Klassik Stiftung Weimar and the Herzog August Library Wolfenbüttel collect, preserve and provide access to sources that are crucial to the study of German literary and intellectual tradition. In all three institutions, digitization of their collections has been an important task to build digital collections and provide worldwide access to this cultural heritage. Furthermore, new approaches in the field of digital humanities have been adopted to strengthen the connection of digital collections with the humanities and cultural studies. All of these goals can be reached easier by cooperation and the use of established tools and infrastructure, which will be demonstrated, based on the example of the implementation of a generic search over collections of all three institutions. For the implementation of the generic search the Data Federation Architecture (DFA) from DARIAH-DE is used.