Paul Fournier (1853–1935) is considered one of the greatest historians of medieval canon law of the last two centuries. Indefatigable, prolific, and meticulous, he opened new paths in research to new generations in a time in which French jurists did not pay much attention to canon law. Fournier’s academic mission was precisely to cover that important intellectual gap, giving new life and light to canon-law science in French public universities. Many of his writings, especially those dealing with medieval ecclesiastical courts and those referring to canonical collections, are of lasting value. His academic footprint has continued through the work of great pupils and pupils of pupils such as Gabriel Le Bras and Jean Gaudemet. As a secondary actor in the religious events related to the French Third Republic, Fournier was able to accommodate his traditional Catholicism to the new social trends and to sow peace at a convulsive time in the relations between the Catholic Church and the French state. The influence Fournier exercised over the general ideas of his time, both in the legal field and in philosophical and moral terms, cannot be minimized.