As commonly used in its moral sense I will, for the purposes of this paper, take the concept of “conscience” to be the inherent ability of every healthy human being to perceive what is right and what is wrong and, on the strength of this perception, to control, monitor, evaluate and execute their actions. Such values as right or wrong, good or evil, just or unjust, and fair or unfair have existed throughout human history and are also shaped by an individual’s cultural, political and economic environment. The medieval penitential literature offers just one such historical snapshot. These manuals or guides for confessors, including prayers, lists of questions to be asked by the confessor, and penances to be assigned for various sins were an integral part of the practice of private penance which began in the Celtic Church and later spread through Europe with the Celtic and Anglo-Saxon missions. Penitential books for use by confessors in private penance appeared in the sixth through ninth centuries. These texts were not as a rule decreed by episcopal synods. Their authority generally rested on the reputation of their compiler or editor. Public penances were assigned for public sins that caused scandal for the church. Private penances were assigned for private sins or matters of conscience. The Penitentials were generally more flexible than the churches’ ancient canonical penitential system which they largely replaced. While later European Penitentials tended to provide more complete guidance for the confessor instead of mere lists of rules and penalties; such instruction is not entirely absent from the earlier Irish texts and ancillary documents. Thus, the goal of penance in the early middle ages was not only sacramental but also didactic. It would have been an occasion to inculcate Christian beliefs, an opportunity to model proper Christian behaviour and by extension a key part of the formation of conscience. As was the case with later expressions of casuistry (Etym. Latin casus, case, or problem to be solved) the purpose of the penitential literature was thus to adapt and apply the unchangeable norms of Christian morality to the changing and variable circumstances of human life albeit in somewhat rudimentary fashion. As such this literary genre and the pastoral practices stemming from it are a valid and worthy object of any historical study and theological analysis concerning the ‘formation of conscience.’