Called by Pope Innocent III in April of 1213 and convened in November of 1215, the Fourth Lateran Council was attended by some eight hundred bishops and four hundred abbots, priors, and heads of collegiate churches, making it, at the time, the largest and most influential council ever assembled by the Western papacy. For historians interested in pastoral care and lay religious experience, canon twenty-one, Omnis utriusque sexus, is emblematic of the Council's reforming agenda. This canon required all Christians aged twelve or older to confess their sins to their ‘own priest’ at least once a year in preparation for receiving the Eucharist at Easter, on pain of excommunication. Confession could be made to another priest only with the permission of one's ‘own priest’. And the priest himself, as confessor, should be a medicus animarum, carefully advising and prescribing penances in order to heal the penitent's moral sickness.

The sacrament of confession, and the theology, legislation and literature that accompanied it, have been the subject of extensive and fruitful scholarship. Confession was for a long time the subject of Protestant-Catholic partisan debate: for Catholics it had developed gradually from the Church's earliest days; for Protestants it was an unbiblical medieval distortion. Protestants in particular made Omnis utriusque sexus, seemingly the first clear and ecumenical mandate for confession in its late medieval form, emblematic of that distortion. They saw the Fourth Lateran Council as a turning point, whereas Catholics emphasised continuity. Since the beginning of the twentieth century the continuity-versuschange debate has continued, but in a different form. Recent scholarship upholds confession as an interface between academic theology and practical religious ministry, or, put more broadly, between the institutional Church and lay society. It is now commonly agreed that theology and canon law were moving rapidly toward Omnis utriusque sexus in the second half of the twelfth century, although in a somewhat disparate manner. The Council is therefore seen as a catalyst for the prioritisation and implementation of extant ideas, rather than an innovation in its own right. Much scholarship on confession after 1215 attempts to trace how and how extensively the Council's directives on annual confession and clerical education in particular were actually carried out on a local level, either through the synodal decrees of bishops or the promulgation of pastoral manuals.