Baker's biographical dictionary of musicians.  6 volumes.  In print.

Online version

Biographical information on performers, musicologists, theorists, composers, music librarians; historical and contemporary.

Encyclopedia of Popular Music  (Online)

Edited by Colin Larkin, "this encyclopedia's 30,000 entries cover all genres and periods of popular music from 1900 to the present day, including jazz, country, folk, rap, reggae, techno, musicals, and world music."

Norton/Grove dictionary of women composers 1 volume.  In print.

Included in: Grove Music Online 

Biographical information on women composers.

Oxford Companion to Music (Online)

Brief articles on musical persons and subjects. 

[Music Reference Book ; ML128.B45 D44] Black music and musicians in the New Grove dictionary of American music and the New Harvard dictionary of music / Dominique-René de Lerma and Marsha J. Reisser Chicago : Center for Black Music Research, Columbia College, 1989.

The Harvard Dictionary Of Music 1 volume. Online.

Brief definitions of music subjects.

Oxford Music Online. 

 The Oxford Companion to Music and the Oxford Dictionary of Music include articles on musical persons and subjects. Part of Oxford Music Online. 

Musical instruments:

The Grove dictionary of musical instruments 2nd edition. 2014.  5 volumes. In print.

Included in: Grove Music Online 

Excellent source for articles on musical instruments. Good bibliographies.

Continuum encyclopedia of popular music of the world. 12 volumes. In print.

Garland Encyclopedia of World Music 10 volumes with accompanying CDs

Garland encyclopedia of world music. (Online version; includes audio.)

Volume 1, Africa

Volume 2, South America, Mexico, Central America, and the Caribbean

Volume 3, The United States and Canada

*Volume 4, Southeast Asia

Includes Indonesia.

*Volume 5, South Asia, the Indian subcontinent

 Volume 6, The Middle East

Volume 7, East Asia : China, Japan, and Korea

Volume 8, Europe

Volume 9, Australia and the Pacific Islands

*Vol 10, The world's music,: general perspectives and reference tools

This encyclopedia has a wealth of good information, but article arrangement is not typical.  Coverage in sections entitled "Issues and Processes" is not clear.  Begin by using the index in each volume as well as the general index in volume 10.  Also use the subsections in the Table of Contents at the front and the index at the back of each volume.