The 16th-century movement for reform of the doctrines and practices of the Roman Catholic Church, ending in the establishment of Protestant churches.

The starting point of the Reformation is often given as 1517, when the German theologian Martin Luther launched his protest against the corruption of the papacy and the Roman Catholic Church, although he was breaking no new controversial ground. In fact, most of the Reformation movements laid stress, not on innovation, but on return to a primitive simplicity. Luther’s theological reading led him to attack the central Catholic doctrines of transubstantiation, clerical celibacy, and papal supremacy. He also called for radical reform of the religious orders. By 1530 the rulers of Saxony, Hesse, Brandenburg, and Brunswick, as well as the kings of Sweden and Denmark had been won over to the reformed beliefs. They proceeded to break with the Roman Church, and set about regulating the churches in their territories according to Protestant principles.

In Switzerland, the Reformation was led first by Ulrich Zwingli, who carried through antipapal, antihierarchic, and antimonastic reforms in Zurich. After his death the leadership passed to Calvin, in whose hands reforming opinion assumed a more explicitly doctrinal and revolutionary tone. Calvinism became the driving force of the movement in western Germany, France, the Netherlands, and Scotland, where in each case it was linked with a political struggle. Calvinism was also the main doctrinal influence within the Anglican Church. In Europe the reforming movement was increasingly checked and balanced by the Counter-Reformation. The era of religious wars came to an end with the conclusion of the Thirty Years War (1618–48).