The Middle Ages formed the basis for modern Europe in many different respects. One of the most important – if not the most important – factor behind the formation of Europe was the Catholic Church: The Church functioned as a model for civil administration and jurisdiction for many emerging nation states, which adopted the principles of the papal administration and jurisdiction. On a political level, the medieval Church played an important role, when the secular leaders, especially in the north and east, conquered new territories in the name of Saints Peter and Paul, using Christianization as their justification. Church and faith, like patron saints, relics, church buildings, and devotional practices in their turn had an important effect on communal coherence and local identities. On a personal and everyday level the Church affected the great majority of the European population: the rites of passage from one stage to another in a person’s lifecycle, like baptism, marriage, and preparations for death were regulated by ecclesiastical norms. Through all these, the Church regulated the yearly rhythm of life and the Christian faith shaped the beliefs and worldviews of individuals, who prayed to saints for help and support, appealed to the papacy in their different kinds of problems, made pilgrimages far away or to the neighbouring parish, and donated property to the Church in their last wills.

Since the Catholic Church was involved in practically every aspect of medieval life, it is impossible to make a comprehensive evaluation of its role and significance for Christians, societies, and cultures. Some large and frequently cited publications regarding medieval history, such as The Oxford Handbook of Medieval Christianity, The New Cambridge Medieval History, or the French Histoire du christianisme, attempt to cover as many aspects of the role of the Roman Church as possible, but its magnitude in medieval life renders these efforts extremely difficult.

Rather than a ‘mission impossible’ of covering all perspectives of Christianity in one book, most medieval historians specialize in one or two aspects of the medieval Church and belief and their roles in different aspects of life. In the course of historiography, those studying different aspects of the medieval Church have moved further and further away from each other: scholars interested in papal administration or canon law rarely meet those interested in the history of crusades or those focusing on hagiographic sources.