The Knights of Columbus Vatican Film Library, housed in Pius XII Library, is one of the premier centers for manuscript research in the U.S. The library has both a large collection of manuscripts on microfilm and a reference collection to support manuscript research. Detailed information is available by clicking on the link.
Georgetown University's The Labyrinth: Resources for Medieval Studies (archived and no longer maintained as of 2021) has a page for Manuscripts.
The sources listed below are only a small sampling of the electronic and print resources available either in the Vatican Film Library or Pius XII Library.
In Principio: Incipit Index of Latin Texts.
Please click "Enter Databases" button on the Brepols Web site, scroll to the appropriate icon and click on it to begin searching. In Principio is a index of approximately 1,000,000 incipits (first few words of text) of Medieval and Renaissance Latin manuscripts.
Iter Italicum.
Electronic version of Paul Kristeller's multivolume listing of "uncatalogued or incompletely catalogued humanistic manuscripts of the Renaissance in Italian and other libraries" (to borrow from the subtitle of the printed work). Both the printed volumes (Z 6611 .H8 K7) and the CD-ROM version (Z6611.H8 K7 1995) of the database may also be consulted in the Vatican Film Library Reference collection.
Latin manuscript books before 1600 : a list of the printed catalogues and unpublished inventories of extant collections by Repertorium edierter Texte des Mittelalters aus dem Bereich der Philosophie und angrenzender Gebiete by