Center for the History of Music Theory and Literature (http://www.music.indiana.edu/chmtl/)
Established in 1998 as a joint venture of Indiana University's School of Music and the Office of Research and the University Graduate School, the Center for the History of Music Theory and Literature (CHMTL) brings together various activities, publications (both electronic and conventional), and projects centered at the School of Music at Indiana University. In addition to its current activities, CHMTL anticipates expansion with additional full-text databases, a new series of publications, conferences, and occasional fellowships for visiting scholars. (from the CHMTL Web page)

Thesaurus Musicarum Latinarum (TML) (http://www.music.indiana.edu/tml/start.html)
The Thesaurus Musicarum Latinarum (TML) is an evolving database of the entire corpus of Latin music theory written during the Middle Ages and the Renaissance. (from the TML Web site)

Thesaurus musicarum italicarum (TMI) (http://www.euromusicology.org/tmiweb/tmiweb.htm)

Lexicon musicum Latinum medii aevi (LmL) (http://www.badw.de/musik/lml.htm)
Dictionary of Medieval Latin Musical Terminology to the End of the 15th Century (from the LmL Web page)

E-texts of LmL Reference Editions
This page lists all texts compiled for the afore-listed LmL textual database and provides links to the electronic editions.

Saggi musicali italiani (SMI) (http://www.music.indiana.edu/smi/)
Designed to extend the Thesaurus Musicarum Latinarum and to continue the endeavor of capturing all texts on music theory and aesthetics in electronic form. saggi musicali italiani [SMI] focuses first and foremost on the major treatises written in Italian, allowing them to be downloaded, browsed, and searched. The database will eventually comprise all printed materials from the Renaissance to the present. (from the SMI Web page)

GENERAL INFORMATION ON MEDIEVAL MUSIC
Eras Online: 450-1450 (Essentials of Music) (http://www.essentialsofmusic.com/eras/medieval.html)
Medieval Music & Arts Foundation (http://www.medieval.org/)
Resources for Medieval Studies (Georgetown University): Medieval Music (http://www.georgetown.edu/labyrinth/subjects/music/music.html)
Links to various sites on Medieval music (http://www.netserf.org/Music/)
Music History: The Middle Ages (Internet Public Library) (http://www.ipl.org/exhibit/mushist/middle/index.htm)
Musical Forms: Plainchant (Classical Music Pages) (Plainchant: (http://w3.rz-berlin.mpg.de/cmp/g_plainchant.html)
Trope (http://www.newadvent.org/cathen/15065a.htm)
Motet (http://w3.rz-berlin.mpg.de/cmp/g_motet.html)

GLOSSARIES OF MEDIEVAL MUSIC
On-Line Reference Book for Medieval Studies: Glossary of Medieval Music (http://www.vanderbilt.edu/~cyrus/ORB/orbgloss.htm)
Glossary of Medieval, Renaissance, and Baroque Music (http://plato.acadiau.ca/courses/musi/callon/1253/glos1200.htm)

PEOPLE
Boethius (c. 480-c. 524) (http://www.mala.bc.ca/~mcneil/tboethius.htm)
Perotin (c.1160-1238) (http://www.mala.bc.ca/~mcneil/perotin.htm)
Guido (c. 995-1050) (http://www.newadvent.org/cathen/07065a.htm)
De Vitry (1291 - 1361) (http://www.classical.net/music/comp.lst/vitry.html)
Machaut (http://www.classical.net/music/comp.lst/machaut.html)
Machaut (1300-1377) (http://www.hnh.com/composer/machaut.htm)
Du Fay (c.1400-1474) (http://www.hnh.com/composer/dufay.htm)
Ockeghem (c.1410-1497) (http://www.classical.net/music/comp.lst/ockeghem.html)

MUSIC THEORY
Thirteenth-Century Polyphony: A Quick Guide to Combinations and Cadences (http://www.medieval.org/emfaq/harmony/13c.html)
Pythagorean Tuning and Medieval Polyphony (http://www.medieval.org/emfaq/harmony/pyth.html)

CHURCH MODES
The Eight Gregorian Modes (http://www.beaufort.demon.co.uk/modes.htm)

TUNING AND TEMPERAMENT
Nicola Vicentino (http://www2.hmc.edu/~alves/vicentino.html)
Ancient Greek Origins of the Western Musical Scale (http://www.midicode.com/tunings/greek.shtml)

GREEK MUSIC AND THEORY
Ancient Greek Music: Bibliography (http://titan.iwu.edu/~classics/music.html)
Greek Music (Catholic Encyclopedia) (http://www.mistral.co.uk/hammerwood/gmusic.htm)
Greek Esoteric Music Theory Charts (http://www.cs.utk.edu/~mclennan/BA/PT/BA/GEM/index.html)
Ancient Greek Music: Audio Fragments (http://www.oeaw.ac.at/kal/agm/)
Plato on Music (http://www.perseus.tufts.edu/cgi-bin/ptext?lookup=Plat.+Rep.+398d)
Plato, Timeaus: Composition of the Soul (http://www.aboutscotland.com/harmony/prop.html)
Aristotle on Music (http://classics.mit.edu/Aristotle/politics.8.eight.html)
Harmony and Proportion: The "Means" (Arithmetic, Harmonic, Geometric) (http://www.aboutscotland.com/harmony/harmony.html)
Ancient Greek Origins of the Western Musical Scale (http://www.midicode.com/tunings/greek.shtml)

GREEK MUSIC THEORY: TUNING AND TEMPERAMENT
Ancient Greek Origins of the Western Musical Scale (http://www.midicode.com/tunings/greek.shtml)
Pythagoras: Music and Space (http://www.aboutscotland.com/harmony/prop.html)
Harmonic Theory and Just Intonation (http://users.rcn.com/dante.interport/hartheory2.html)
Harmony and Proportion: The "Means" (Harmonic, Arithmetic, Geometric) (http://www.aboutscotland.com/harmony/harmony.html)
Pythagorean Tuning and Medieval Polyphony (http://www.medieval.org/emfaq/harmony/pyth.html)
Nicola Vicentino (http://www2.hmc.edu/~alves/vicentino.html)

CHANT RESOURCES
Princeton University Gregorian Chant Home Page (http://www.music.princeton.edu/chant_html/)
Gregorian Schola Chant Links (http://comp.uark.edu/~rlee/otherchant.html)
Database for Latin Ecclesiastical Chant (http://publish.uwo.ca/~cantus/)
Internationale Gesellschaft für Studien des Gregorianischen Chorals (http://www.aiscgre.de/)
Influence of Gregorian Chant to Present Times (http://www.samedaymusic.com/library--influenceofgregorianchant)

AUDIO LINKS
Ancient Greek Music (http://www.oeaw.ac.at/kal/agm/index.htm)
The Internet Renaissance Band (http://www.csupomona.edu/~jcclark/emusic/medieval.html)
The Classical Music Page: Early Music (http://www.midiworld.com/earlymus.htm)
Gregorian Schola: Chant Sounds (http://comp.uark.edu/~rlee/otherchant.html#sounds)