The author investigates into the history of the main military library of the Russian Empire. In the mid 19-th century, the General Staff Library became one of the largest book depositories in Russia. The author sets the goal to review the main events related to the library during the period when F. F. Kruse and A. N. Petrov were heading the institution. This period was characterized by consistent collection development and collaborations with military historians, and by the new trends of expanding openness of the institution. Owing to the reform by Dmitry Milyutin, Minister of War, the library became accessible for all military personnel a nd, through s pecial o rder, f or c ivilians. T he s ources f or the s tudy a re unpublished materials from the Russian State Military Historical Archive. Based on these sources and literature, the author describes the efforts of the librarians F. F. Kruse and A. N. Petrov, analyzes the internal structure of the institution, the sources for collection development and structure. Despite the fact that the institution was run by professional soldiers – the above-mentioned librarians had a military education, and Petrov even took part in the Crimean War – the library was developed properly and performed efficiently.