The early-fourteenth-century St Gall Passion Play comes from the Central Rhineland. Unfortunately its music (over one hundred Latin and German chants) is given in the manuscript only as brief incipits, without any musical notation. This interdisciplinary study reconstructs the musical stratum of the play. It is the first full-scale musical reconstruction of a large German Passion play in recent times, using the latest available scholarly data in drama, liturgy and music. It draws conclusions about performance practice and forces, and offers a sound basis for an authentic performance of the play. The study applies musical and liturgical data to the problem of localizing the play (the first time this has been systematically attempted), and assesses how applicable this might be to other plays. It presents a detailed study of the distinctive medieval liturgical uses of three German dioceses, Mainz, Speyer and Worms. The comparative approach suggests how the music of other plays might be reconstructed and understood, and shows that a better understanding of the music of medieval drama has much to teach us about other aspects of the genre. The book should be of interest to literary scholars, theatre historians, musicologists, liturgical scholars, and those involved in the performance of early drama.