William Peraldus (Latin: Guillelmus Peraldus, French: Guillaume Peyraut) was a French Dominican friar and theologian. He served as prior of the Dominican convent in Lyon and was one of the most widely read moral theologians of the later Middle Ages. His two great works, the Summa de Virtutibus and the Summa de Vitiis, were composed in the 1230s–1250s and circulated together as the Summa de Virtutibus et Vitiis. These practical handbooks for preachers and confessors offered systematic treatments of the virtues and vices, drawing on Scripture, the Church Fathers, and Aristotle. They were among the most copied and printed texts of the medieval period, surviving in hundreds of manuscripts and numerous incunabula editions.
