International Inventory of Musical Sources (RISM)
RISM is a multi-national, non-profit organization with the aim of documenting extant musical sources (in manuscript or printed form) around the world. These sources are housed in libraries, archives, monasteries, schools and private collections. The organization was founded in Paris in 1952. It is the largest and sole organization operating globally that documents written musical sources. RISM records what exists and where it is held.
Also see: www.rism.info
Also see: opac.rism.info