William of Auvergne, bishop of Paris from 1228 until 1249, is one of the major figures in the medieval history of learned magic and demonology. In many later writings on these topics from the fourteenth or fifteenth centuries, one finds his name cited as often as, if not more often than, that of his great slightly later contemporary Thomas Aquinas. Yet while scholarship on Thomas and this thought fills bookshelves, the bibliography on William is dramatically thinner. As de Mayo notes, the standard biography of William remains Noël Valois's Guillaume d'Auvergne, Évêque de Paris (1228–1249): Sa vie et ses ouvrages, published in 1880. He receives thirty-five pages in Lynn Thorndike's encyclopedic History of Magic and Experimental Science (volume two, 1923), but de Mayo's book is the first to provide a monographic study of his magical and demonological thought.