Throughout the Middle Ages and early modern Europe theological uniformity was synonymous with social cohesion in societies that regarded themselves as bound together at their most fundamental levels by a religion. To maintain a belief in opposition to the orthodoxy was to set oneself in opposition not merely to church and state but to a whole culture in all of its manifestations. From the eleventh century to the fifteenth, however, dissenting movements appeared with greater frequency, attracted more followers, acquired philosophical as well as theological dimensions, and occupied more and more the time and the minds of religious and civil authorities. In the perception of dissent and in the steps taken to deal with it lies the history of medieval heresy and the force it exerted on religious, social, and political communities long after the Middle Ages. In this volume, Edward Peters makes available the most compact and wide-ranging collection of source materials in translation on medieval orthodoxy and heterodoxy in social context.