In the final years of the fourteenth century, waves of persecution shattered German-speaking Waldensian communities, with the scale of inquisitions matching or even greater than the better-known trials in southern France. In the middle of the persecution was the influential and enigmatic figure of the Celestine provincial and inquisitor of heresy, Petrus Zwicker (d.after 1404). 0His surviving texts and inquisition protocols offer a fresh, intriguing picture of the medieval repression of heresy. Zwicker was an accurate and intelligent interrogator with direct access to the Waldensians' sources and knowledge. But although he is one of the most effective inquisitors of the Middle Ages, he was even more important as the author of anti-heretical texts. His Cum dormirent homines became a standard work on Waldensianism in the fifteenth century (and this study attributes another anti-heretical treatise, the Refutatio errorum, to him). With his unique biblicist and pastoral style, Zwicker struck the right note at a moment when the Church was in crisis. His texts spread rapidly, they were preached to the people and translated into German, and helped to build the fear of heresy, anti-clericalism and disobedience in the years of the Great Western Schism. 0This book is the first full-length study on Zwicker and his significance to the history of heresy and its repression. It offers a meticulous analysis of the sources left by him and teases out new, ground-breaking discoveries from careful examination of previously poorly known manuscripts.