Early reference sources
Some composers' and performers' reputations wane over time, and they may no longer be given entries in current reference works. This makes older reference works valuable sources of information on persons who are little known today.
Some early biographical dictionaries in the Library:
Gerber, Ernst Ludwig. Historisch-biographisches Lexikon der Tonkunstler. Published 1790-1834.
Riemann, Hugo. Musik-Lexikon. Orignally published 1882 (we have 10th ed.).
Eitner, Robert. Biographisch-bibliographisches Quellen-Lexikon der Musiker. Originally published 1900 (we have reprint of 2nd ed.).
Pazdirek, Franz. Universal-Handbuch der Musikliteratur. Published 1904-1910.
Foreign reference sources
An Italian or French encyclopedia is likely to have entries for more Italian or French composers, performers, etc. than an Engish-language reference work.
Some foreign music encyclopedias in the Library:
Die Musik in Geschichte und Gegenwart (MGG).
Dizionario enciclopedico universale della musica e dei musicisti.
Encyclopedie de la musique et dictionnaire du Conservatoire (edited by A. Lavignac).
Diccionario de la música española e hispanoamericana.