Most of the medieval canon law dealing with heresy, magic, and superstition is found in CC. 23–26 of Gratian’s Decretum, the so-called causae hereticorum, also in C. 33 q. 1, in book 5 of the Liber extra of Gregory IX, in later decretals and conciliar canons, and in the broad literature of canonist commentaries discussed elsewhere in this volume. In one sense, of course, these offenses belong to criminal law and fall into the categories of criminal legal procedure and of mixed temporal and spiritual jurisdiction. In another sense they constitute unique problems of theology, including demonology, and therefore influenced canon law in perhaps more complex ways than some other topics