The form of confession is a genre of religious instruction that circulated widely in the fourteenth and fifteenth centuries in northern Europe, especially in England, in the wake of the Fourth Lateran Council's official pronouncement that all Christians must confess their sins to a priest at least once every year. The form of confession was the most grassroot kind of text that taught the grammar of sin to a confessing society. No other kind of pastoral literature comes as close as the form of confession to representing what was to be said by the penitent in the practice of confession. The genre thus offers a compelling entry point for exploring religious history from the ground up. Despite its value to scholars of medieval religion, history, and literature, this genre has nearly escaped the notice of modern critical attention. Functioning as a mirror for self-examination, the form of confession voices through a first-person speaker the manifold variety of sins that might be acknowledged by the penitent. Reading the form of confession, or hearing it read aloud, penitents could recognize in the wide-ranging avowals of sin, in a voice that was to become their own voice, the sins they had committed, so that they could articulate them to their confessor. The form of confession was thus a written text that served an oral purpose, as an aid to the actual practice of auricular confession. This dissertation introduces and defines the genre and then documents in a catalogue all the known examples of Latin, French, and English forms of confession from ca. 1200 to ca. 1500, including Latin and Old English precursors dating back to the ninth century. In documenting the genre of the form of confession more fully than has ever been done, this study provides a substantial body of new evidence that can be used to study various questions of medieval confessional practice.