This article deals with the practice and theory of penances imposed on heretics by inquisitors in southern France before 1250. At first inquisitors offered a simple choice between penance as proof of conversion or death by burning. Lay resistance forced a subtler approach whereby penitents were removed from the local community in order to be gradually reintegrated into the wider Catholic one. The construction of prisons and the imposition of crosses helped turn inquisitors into an institution. From being a means to the destruction of organised heresy, they became a permanent police force of doctrinal orthodoxy.