This study presents a critical edition of a treatise "Contre les Devineurs" by friar Laurens Pignon. The magicians and astrologers who frequented the courts of Burgundy and France during the reign of Charles VI, rendering their dubious services to king and nobles, induced the friar to write the treatise. In it, Pignon demonstrates the dangers and deficiencies of divination, by means of theological and philosophical arguments derived from Aquinas. This study attempts to reconstruct the historical and intellectual context of the treatise by examining the role of magic and astrology at court. In three appendices editions of supplementary documents are supplied: a confession of a court magician, two divinatory texts, and a fictional prognostication on the house of Burgundy.