The library of the Museum of Warmia and Mazury in Olsztyn initiated its work immediately after the end of the World War II. The first volumes in its book collection were German books from abandoned manor houses, churches and public buildings. They were taken to a depot established in the castle. Most volumes came from the collections of state and institutional bodies, especially those once gathered in Königsberg. The number of Königsberg volumes held in the collection of the Library of the Museum of Warmia and Mazury in Olsztyn is estimated at about 1,000 titles, including old prints, publications published after 1801 and continuous publications. The provenance marks there are currently being studied in detail as part of the project ‘Pre-War Book Collections as a Source for the History of Warmia and Mazury’.