The collections of Martin-Opitz-Library, founded in 1948, cover the history and culture of Germans in East Central, Eastern and Southeastern Europe. An emphasis of the collection is the historical eastern provinces of Prussia. It is the largest scientific library of this kind in Germany.

Martin-Opitz-Library collects the written records of the history and culture of Germans in Eastern Europe. Generally, the items cover an area between the Baltic States and the Balkans, where Germans lived alongside other nationalities (for example, Bohemia, Moravia, Transylvania, Banat), but the main focus of the collection lies on the historical eastern provinces of Prussia (Silesia, Pomerania, East and West Prussia, East Brandenburg).

With approximately 350,000 titles, 12,000 periodicals and 9,500 maps Martin-Opitz-Library is offering a wide range of literature, both in German and in different Slavic languages. The library has the function of a central library for the mentioned regional collection area.
Thematically, the library collects mainly history, especially historical geography, local and family history as well as church and religious history (much of it Judaica). Additionally, fiction and specialist literature on German language and literary studies connected to the area are part of the inventory. Another key aspect is related to relevant literature on migration and minority research: flight, expulsion and integration of German expellees and the integration of immigrants.