The Directorium Inquisitorum is Nicholas Eymerich's most prominent and enduring work, written in Latin and consisting of approximately 800 pages, which he had composed as early as 1376. Eymerich had written an earlier treatise on sorcery, perhaps as early as 1359, which he extensively reworked into the Directorium Inqusitorum. In compiling the book, Eymerich used many of the magic texts he had previously confiscated from accused sorcerers. It can also be considered as an assessment of a century and a half of official Inquisition in the "albigensian" country.

Nicholas Eymerich was a Roman Catholic theologian in Medieval Catalonia and Inquisitor General of the Inquisition in the Crown of Aragon in the later half of the 14th century. He is best known for authoring the Directorium Inquisitorum, that mostly summarized previous texts and mores.