The present study of the medieval Inquisition makes no pretense either to exhaustiveness or to originality. It may be said to take the form of a study rather than a history - a study of the particular problem of medieval heresy and of the means taken to combat it. The author makes no claim to have written a historical textbook on the medieval Inquisition. Contents: spirit of the middle ages; rise of the heresies; Languedoc and the crusade; establishment of the inquisition; inquisition in action; major penalties; crosses, pilgrimages and other sentences; inquisition in Europe; on the beliefs and practices of the Albeginsian heretics.