T HE conflict of official Christianity with the surviving pagan beliefs and practices of the common people is a highly important aspect of medieval history, and one of absorbing interest. The sources for the subject are extensive, including sermon literature, treatises on discipline and morals, synodical decisions, the public laws of the Irish, Welsh, English, Franks and Visigoths, and the Scandinavian codes, lives of the saints, descriptions of countries and their inhabitants, the records of the Inquisition, and a wide range of medieval popular literature. The Libri Poenitentiales, which constitute a museum of medieval misdemeanors and errors, also contain a body of materials in this field.