Music and Sheet Music

• Petrucci Music Library Over 200,000 open access scores
• Beethoven-Haus Bonn: Digital Archives Beethoven music manuscripts, first editions, letters and pictures.
• Chopin Early Editions: Digitized images of scores in the University of Chicago Library's Chopin collection
• Corpus Mensurabilis Musicae Electronicum Utrecht University's CMME project represents a collaborative development effort to offer free online access to new, high-quality early music scores.
• Digital Mozart Edition: Neue Mozart-Ausgabe Offers the musical text and the critical commentaries of the entire Neue Mozart-Ausgabe.
• Bavarian State Library digitized music scores
• Choral Public Domain Library: includes scores, sound files, texts, and translations
• National Library of Denmark digitized music scores
• Digital Image Archive of Medieval Manuscripts
• Digital Music Collections: list maintained by Harvard University
• Gallica: Bibliothèque numérique: digital collections from the Bibliothèque nationale de France
• Juilliard Manuscript Collection Composers included in this collection include Bach, Beethoven, Brahms, Copland, Debussy, Liszt, Mozart, Schubert, Schumann, and Stravinsky
• Musical Theatre Scores: University of Illinois Urbana-Champaign
• Musopen: contains scores and MIDI files
• Mutopia Project: contains scores and MIDI files
• Sibley Music Library (Eastman School of Music/University of Rochester): scores and books in the public domain. Many of these are unique to the Sibley Music Library collection.
• Virtual Music Rare Book Room: University of North Texas
• Web Library of Seventeenth-Century Music: new editions of previously unknown 17th-century sacred and secular compositions
• Wikipedia list of online music databases

Music Theory

• Bach's Canons and Fugues (no longer) maintained by Timothy A. Smith
• Big Ears Online Ear Training
• Center for the History of Music Theory and Literature at Indiana University
• Dissertations in Music Theory from Music Theory Online
• Music Analysis and Program Notes Index from the University of Tennessee, Knoxville
• Music Theory Resources
• Schenker Guide maintained by Tom Pankhurst
• The Society for Music Theory
• Teoria Music Theory Web maintained by José Rodríguez Alvira
• Thesarus Musicarum Latinarum Medieval and Renaissance Music Theory Treatises
• Tonal Centre An interactive site for music composers and theorists which explains and demonstrates some of the key concepts of tonality; including chords, scales, cadences, and modulation.