If the traditional history of heresy in the Middle Ages has long been confused with that of the socially excluded, the recent approach focuses more on the various authorities who, at the heart of power, develop orthodoxy. Heresy exists only because orthodoxy first decided it. This inquiry is based on the conviction that it is still by being at the margins of heresy, in contact with neighboring reprehensible activities, such as usury, witchcraft or political rebellion, that we can best to grasp the principles and mechanisms of the fabrication of heresy.