collection of nearly 3,800 texts touching on all areas of church discipline and regulation compiled by the Benedictine monk Gratian about 1140. It soon became the basic text on which the masters of canon law lectured and commented in the universities.

The work is not just a collection of texts but also a treatise attempting to resolve the apparent contradictions and discordances in the rules accumulated from different sources. When necessary, Gratian had recourse to the Roman law and made extensive use of the works of the Church Fathers and of ecclesiastical writers.

For centuries the Decretum was the text on which the teaching of canon law in the schools was based. It was glossed and commented on by the most illustrious canonists; it became the first part of the Corpus Juris Canonici, the great body of canon law; and it served as an important source for the official codification of canon law in 1917 and its revision in 1983.