Internationales Quellenlexikon der Musik . Saur Series A Vol. Musikhandschriften nach 1600. Unfortunately the accompanying handbook is not as helpful as it could be, lacking sufficient examples, search possibilities, a listing of symbols, etc. Although the interface is offered in German, French, and English, and some information is provided only in German, the content itself is only in English.
Descriptive information is inconsistent and often too brief, resulting in unsatisfactory searches.
Details regarding watermarks, paper size, and type of script would have also been useful. Too much information is made available only by looking at each title separately, and it would have been desirable to have incipits for more than just the upper voice. Musical notation is not given if it is available in any edition for a given work. This is a venerable tradition, and it is time to give it up. In terms of content, this work is a step in the right direction.