The oath of innocence, or purgation, constituted a part of canon law for almost a millennium. This book seeks to reconstruct the history of the oath of purgation specifically from the perspective of canon law. Priests of the Church were required to swear their innocence when charged with any criminal offence for which evidence of guilt was lacking. At this time, the canonists also developed the notion of infamia facti, a concept of social disrepute with real legal significance. Within a short space of time this inspired the most significant innovations in medieval legal procedure: the introduction of the inquisitorial process, the elaboration of a canonical theory of legal presumptions and the justification of judicial torture. The history of the oath of purgation thus provides a unique perspective from which to observe the transformations in law and legal culture which occurred throughout the course of the Middle Ages.