This seminar explores the codicological and documentary evidence for reconstructing the contents and organisation of the libraries of ecclesiastical and academic institutions in the Middle Ages. It provides an introduction to two key resources for the study of medieval libraries: N R Ker’s Medieval Libraries of Great Britain (and its online counterpart MLGB3) and the Corpus of British Medieval Library Catalogues, before focusing upon the remarkable record of the library of the Augustinian canons of Leicester Abbey that survives in the Bodleian as MS Laud. Misc. 623.