Martin-Opitz-Library, Research library in Herne, Germany.

The Martin-Opitz-Library is a research library in Herne that holds approximately 360,000 books, 12,000 periodicals, and 10,000 maps. The collection focuses on German cultural traditions and histories across Eastern Europe.

The library's collection began with the Bücherei des Deutschen Ostens, run by the city of Herne since 1948. On 25 September 1989, North Rhine-Westphalia and Herne established the Martin-Opitz-Bibliothek foundation with federal funding, taking over its 80,000 volumes. It has been an affiliated institute of Ruhr University Bochum since 28 September 2021.

The collection reflects connections between German-speaking communities and Eastern Europe, with materials in multiple languages that document these historical relationships. Visitors can explore the cultural diversity and lived experiences of these regions through the holdings.

The library offers free access to its materials and participates in a Books-on-Demand network that provides digitized works from before 1900. Visitors find all necessary research facilities and specialist guidance on-site for their inquiries.

Alongside the association archive of the Working Group of East German Family Researchers, the library holds the Archive of Germans from Central Poland and Volhynia, the Galicia-German Archive and the Archive of the Historical Society of Volhynia. These holdings document German settlement communities whose records are otherwise scattered.