The RILM organization (Répertoire International de Littérature Musicale) began in the 1960s and has been growing ever since. It is a major resource and one that covers many aspects of music research.
The primary content is scholarly and Western focused, though this is expanding as auxiliary fields grow and are increasingly accepted as mainstream.
If you are looking for trade publications (magazines like Strings or Opera News), or are researching ethnomusicology or popular music, you will need to supplement your search with additional databases.
RISM - Répertoire International des Sources Musicales
RISM is a vast project seeking to document musical sources in libraries, archives, and other institutions. It is an essential tool for anyone doing primary source research in the common practice period. Additionally, specialty indexes in Series B have expanded RISM beyond its core focus.
Until recently, RISM consisted of multiple parts that were accessed and used differently, but all of Series A and Part I of Series B have been combined into a single online database, now available without a subscription, and updated regularly.
It is helpful to understand the different series as they were conceived to know the scope of what you can find in RISM. Additionally, the print volumes can be easier to use in some circumstances, and most of Series B is only available in print. All print volumes may be found in the reference section: ML 113 .I6
RISM Series A - Part I
RISM Series A - Part II
RISM Series B
RISM Series C