Libraries have been fundamental to all humanistic inquiry since antiquity. Catalogues compiled in the middle ages provide the means to understand what books were available and how they were organized and used, even though the libraries themselves were dispersed centuries ago and most of the actual books lost.
Some itemize all texts in each volume and so provide a full picture of the contents of a library at a particular time, others inventorize books as objects and refer only to the principal text contained; for some libraries there survives a whole series of catalogues, allowing one to trace the development of the collection, while others were dynamic documents, added to and altered by successive librarians over a long period. Such documents can be very difficult to understand, demanding a great deal of knowledge (both of texts and manuscripts) to make sense of them. When their medieval references to individual texts are understood, however, they provide an essential perspective on medieval intellectual life. They show what texts might be available at a particular period in a certain sort of institution, revealing what a scholar there might have had access to, and they allow us also to see how knowledge was organized. They underpin our knowledge of monastic learning and of university curricula. It is possible to trace surviving books that bear evidence of their medieval library-provenance; in rare cases we find enough survivors with shelf-marks to begin to reconstruct the organization of the library. Medieval catalogues make this possible for many more libraries than do surviving books, and, almost more importantly, for libraries of different kinds. One can form a picture of a typical library of a certain kind in a certain period, and one can see the particular contents of some unusually good libraries. Every effort is made to trace where the medieval manuscript survives, since comparison with the book itself enhances one’s reading of the medieval catalogue.