Published since 1977, the Marburg Index is both a reference work and guide to art in Germany. The photographic material is organized by location of the respective object; photographs of individual locations are classified by city, ecclesiastical building, secular building, and collection. In 1977, cataloguing commenced on the basis of material provided by the Bildarchiv Foto Marburg and the Rheinische Bildarchiv based in Cologne. Subsequently, an increasing number of photographic collections from other institutions (such as regional offices for the preservation of historical monuments (Denkmalamt), museums, archives, picture and film archives) were incorporated in the Index.