Block books or xylographs are illustrated books of a relatively small volume, crafted in the 15th century in a wood-cutting procedure. They mark a transition from illuminated manuscripts to illustrated printed books. They belong to the rarest and consequently most valuable collectibles of libraries. On a worldwide scale libraries hold around 600 copies of around 100 editions of 33 different works. Until today block books pose many questions to researchers in the fields of historical bibliography, art history and philology regarding the age of the individual prints, their regional origin and their classification regarding the traditions of handwritten and graphically printed text and image publication. However, scholarly research into block books is further complicated by their highly problematic conservation state. Since the paper sheets are frequently damaged by colour corrosion, the books can be made physically available to scholars for perusal only by way of exception In the project, which was funded by the DFG from 2009 to 2013, the rich block book holdings in 14 Bavarian collections (libraries as well as museums, in state, church and private ownership) were described at a high bibliographic level and reproduced and made accessible in their entirety in high-quality digital recordings: over 90 block books and block book fragments were digitised and most of them catalogued for the first time.