The following list is a logical sequel to the bibliography of printed catalogues published some years ago (Traditio VI [1948] 227-317), and it serves the same purpose, namely to facilitate the study of Latin manuscript books, which is important to classical and patristic scholars as well as to historians of the Middle Ages and of the Renaissance. A continuing exploration of the extant collections still leads to the discovery of unpublished writings, brings to light copies of known texts that are of special interest, or at least gives statistical evidence for the diffusion of certain well known works at the time when the manuscript book was the predecessor or rival of the printed book. Information on the general importance and content of the various manuscript collections proved essential both for the project of ‘Medieval and Renaissance Latin Translations and Commentaries,’ which has been undertaken by a group of scholars under the auspices of several learned societies, and for a summary list of philosophical and literary manuscripts of the Renaissance which I am preparing for the Warburg Institute in London. The present list is an outgrowth of these two undertakings, and it was first compiled in a less elaborate fashion for the former project and issued in mimeographed form under its auspices in 1951.