Music Index has references to articles in over 600 international music journals.

RILM indexes journal articles and other types of material such as books, dissertations and festschriften.

Education Abstracts and ERIC help in finding scholarly articles and reports that pertain to music education.

Digital Dissertations (Dissertation Abstracts) index master's theses and doctoral dissertations for North America and Europe since 1861. Titles published since 1997 are available in PDF digital format and have 24 page previews available.

More on these and other recommended databases here.

Items that begin their call numbers with M2 are collections of musical sources that are not necessarily all composed by the same person.

Example:
• M 2 .A535 F7 — French Secular Music of the Late Fourteenth Century

Items that begin their call numbers with M3 are the collected works of individual composers.

Example:
• M 3 .B58 — The Complete Works of William Billings

The collected works will be in alphabetical order according to the composer's last name.

Some sets of collected works have their own indexes, while others do not. To find out which volume of a composer's collected works contains the piece you want to see, consult the works list at the end of the composer's article in The New Grove Dictionary of Music and Musicians (older edition in Ref. ML 100.N48 v.1-20) or consult Anna Harriet Heyer's Historical Sets, Collected Editions, and Monuments of Music: A Guide to Their Contents (Ref. ML 113 .H52 1980).