RISM's catalog is a finding aid for music manuscripts and prints; the online catalog includes Series A/1 and A/II (Music Manuscripts after 1600) and parts of B/1 as well as a list of library sigla. Other components can be found in print in the Orwig Music Library.
"The Music Division is one of the world's preeminent music collections--documenting the art of music in all its diversity - classical and opera as well as the whole spectrum of popular music including spirituals, ragtime, jazz, musical theater, film, rock and world music. While the division contains many scores and manuscripts from centuries past, its curatorial mandate is an activist one, placing major emphasis on capturing the creative output of contemporary composers."
Since its founding in 1998, "the purpose of the Digital Image Archive of Medieval Music (DIAMM) [has been] to obtain and archive digital images of European sources of medieval polyphonic music, captured directly from the original document."