See the Composer Editions section of this page

An excellent place to start!

This website is a portal to information about and images of worldwide collections of medieval polyphonic music manuscripts (the resource does not include plainchant). The music and the manuscripts date from approx 800 to 1550 but we do have images from a few prominent later sources. This website includes detailed information for all the known sources of European polyphonic music (which is almost entirely vocal) and high-quality colour images of some manuscripts.

ViFaMusik, the central portal for music and musicology, allows you to access an extensive digital library containing the latest scholarly research and online resources. Using a single search engine you can find bibliographical data, full text data, and information about experts in musicology. ViFaMusik is “work in progress” and is continuously being extended.