This Repertorium is part of a European initiative called SERMO, which is distinct from the present eponymous book series, and is a series of separate projects making available information about sermons in various medieval vernaculars through the provision of systematic catalogues or repertoria. Containing details of over one thousand Middle English prose sermons in more than one hundred and fifty manuscripts, mainly from the late fourteenth and fifteenth centuries, the current Repertorium incorporates sermons already published alongside those that remain unedited. Each entry contains a concise manuscript description, followed by a detailed analysis of each catalogued sermon under various headings, including authorship, occasion, summary of content, exempla, and biblical citations: the whole work is supported by an extensive set of indices. By representing the texts in a consistent and streamlined manner the Repertorium will serve as a stimulus to future editions, facilitate comparative study and open up new research questions. This work of reference, which provides an overview of the whole corpus of Middle English prose sermons, is not aimed just at sermon specialists but at all scholars interested in medieval historical, literary, and religious culture.