While not primarily known for their preaching today, the Fathers of the Early Church, Augustine, Leo Magnus, Gregory the Great and many of their contemporaries, were prolific preachers. Their sermons were widely disseminated throughout medieval Europe in the form of sermon collections, preserved in thousands of manuscripts. This was a highly dynamic tradition, in which patristic sermons were continuously reorganised, rewritten, and used as inspiration for new sermons. The PASSIM project places this under appreciated part of the patristic heritage center stage and aims to execute the first large-scale analysis of the formation and spread of patristic sermon collections in medieval Europe. The project is developing a digital network of manuscripts, using well-tried principles from the field of textual criticism. Building on this network, PASSIM pursues three lines of inquiry: the customizing of standard liturgical collections as indicative of individual purposes and contexts, the impact of transmission on the popularity of patristic sermons, and pseudo-epigraphic sermons as revelatory of medieval perceptions of the Church Fathers. In this lecture, Shari Boodts, PI of PASSIM, will introduce the project’s aims and research questions, give a first glimpse at the database of medieval manuscripts the team is developing, and show the relevance of its methodology beyond the field of patristic and medieval sermon studies.