• AMG All-Music Guide
• The American Institute of Musicology
• American Music Resource
• Carolina Classical Connection
• Classical Net
• Concise History of Western Music, 2nd. Edition
• Essentials of Music
• Library of Congress Performing Arts Encyclopedia
• Music at UCC: Web Resources for Research in Music
• MusicWeb Encyclopaedia of Popular Music
• Worldwide Internet Music Resources
• Yahoo! Music

Composers (See also Music Eras)

• Classical Composers Database
• The Living Composers Project
• Women Composers

• African American Music and Culture
• African Music Encyclopedia
• American Roots Music
• The Blues
• Ethnomusicology, Folk Music, and World Music
• Ethnomusicology Resources on the Web
• Folk Music Index
• Index of Native American Music Resources on the Internet
• Internet Chinese Music Archive
• Islamic & Middle Eastern Music & Dance 
• Jewish Music WebCenter
• Latin American Music Center
• Middle Eastern Culture
• Music in the Digital Library of Appalachia
• National Geographic World Music
• Society for Ethnomusicology

Instruments

• CHICO Instrument Encyclopedia
• Encyclopedia Smithsonian: Music and Musical Instruments
• Medieval and Renaissance Instruments
• Musical Instrument Museums and Collections
• The Pipe Organ

Music Eras

Ancient

• Ancient Greek Music
• Evidence of Harmony in Ancient Music
• Music of the Ancient Near East

Middle Ages & Renaissance

• Medieval Music & Arts Foundation
• Music of the Renaissance (Audio Files)
• Renaissance Music Links

Baroque

• Baroque Era Music Links
• Baroque Music Page
• Baroque Music Sampler
• George Frideric Handel
• The J.S. Bach Home Page

Classical

• Classical Period Music Links
• Ludwig Van Beethoven: The Magnificent Master
• The Mozart Project
• Music of the Classical Period at the Classical MIDI Connection
• Research Centre Beethoven-Archiv

Romantic

• Franz Liszt Project
• Fryderyk Chopin
• Johannes Brahms WebSource
• Richard Wagner Archive
• Romantic Era Music Links
• Romantics Unbound: Romanticism in Music

20th Century

• American Popular Music 1900 to 1950
• A Passion for Jazz!
• Rock and Roll Hall of Fame and Museum
• Twentieth Century Music Links

Musical Theater, TV and Film

• Broadway: The American Musical
• Cyber Encyclopedia of Musical Theatre, TV and Film
• Internet Broadway Database
• Library of Congress Presents...Music, Theater, & Dance
• Lortel Archive: The Internet Off Broadway Database

Music Theory and Composition

• Alexander Technique for Musicians
• Good Ear - Online Ear Training Site
• Guide to Schenkarian Analysis
• Musical Intervals Tutor
• The Orchestra: A User's Manual
• A Practical Guide to Musical Compositon
• Ricci Adams' Musictheory.net
• Society for Music Theory
• Solomon's Music Resources
• The Tonal Centre

Opera

• All About Opera
• American Opera
• The Aria Database
• Lyric Opera of Chicago
• The Metropolitan Opera: Met History
• Operabase
• Opera Glass
• OperadiO
• Opera Today
• Stories of the Operas

Scores

• African-American Sheet Music, 1850-1920
• Chopin Early Editions
• Digital Image Archive of Medieval Music (DIAMM)
• Digital Mozart Edition
• E. Azalia Hackley Collection
• Harvard College Library Digital Scores Collection
• Historic American Sheet Music: Rare Book, Manuscript, and Special Collections Library, Duke University
• Lester S. Levy Collection of Sheet Music
• Music for the Nation: American Sheet Music
• Sheet Music Consortium
• Songfile
• UNC-Chapel Hill: 19th Century American Sheet Music Digitization Project
• VARIATIONS Prototype: Online Musical Scores