a reply in writing by the pope to a particular question of church discipline that has been referred to him. In modern usage, such a document is referred to as a rescript (reply). Decretals issued in response to particular questions were authentic decisions for the case in question only and did not have the force of general law. This is true of rescripts in modern church law. Nevertheless, the decretals exercised enormous influence on the development and interpretation of church law because of their frequent application to the solution of analogous situations. At the same time, some decretals became general church law by decree of a pope.

The name decretalist was applied to commentators on the law of decretals as well as to students of the decretals. The title was first used at the University of Bologna, where the decretals served as the text in the study of canon law. Among the most famous and influential of the decretalists were Tancred (d. c. 1234), archdeacon of Bologna, best known for his work on church marriage law and his manual of ecclesiastical procedural law; Henry of Susa (d. 1271), cardinal bishop of Ostia, known as the “king of law” and author of a “Golden Summary” (Summa Aurea) of the titles of the decretals; St. Raymond of Peñafort (Raymond of Peñafort, Saint) (d. 1275), a Spanish Dominican who compiled the Decretals of Gregory IX at Gregory's direction; and Joannes Andreae (d. 1348), a married lay professor of the decretals at the University of Bologna, who is regarded as the father of the history of canon law.