The collection of more than 2,200 early printed music sources – collections and individual printed music – from the 16th and 17th centuries with polyphonic works preserved in the Bavarian State Library is of worldwide range. Many of the sources stem from the earliest court library of the Bavarian electors, founded in 1558. From that time, much diligence had been expended to enlarge the music collection. Since February 2012, all printed music sources with polyphonic works from the 16th and 17th in the collections of the BSB are object to a project that focuses on high quality digitization from the original sources, profiled description in the catalogue OPACplus of the BSB, enrichments for the digital presentation and free access on the internet. The project is substantially funded by the German Research Foundation (DFG) in its Cataloguing and Digitisation Programme. The bibliographic descriptions of the international standard bibliographies for printed music Répertoire International des Sources Musicales (RISM) refer to the Munich sources with the siglum D-Mbs. Most of the music prints from the 16th and 17th centuries have been published in the manifestation form of part books. In the sources from the primary library collections we find them, bound together to collections of up to 20 sources, in voluminous part books. The remaining printed music sources represent all forms of manifestation in their centuries: Lute and organ tablatures, printed choir books, musical broadsides, polyphonic hymn books, music theory containing complete polyphonic works, occasional settings inserted in funeral or wedding sermons or poetry editions, and full scores. The OPACplus of the BSB and the FachOPAC Musik are the main research tools for the profiled catalogue entries, including access to the digitized form of the musical sources. The project includes an adequate online presentation tool for part books, developed by the Munich Digitization Center: All part books of one music publication (one bibliographical entity) will be shown simultaneously on one screen. The Partbook-Viewer is an additional presentation tool of the project. It contains several navigation tools like turning pages, zoom, moving and hiding functions and an elementary search interface. The task bar contains a button to switch to the standard viewer of the Bavarian State Library. From there, it is possible to switch to the DFG-viewer, a surface equipped with several functions like the presentation of two face-in-face pages on one screen.