The Ninety-five Theses was a list of propositions for an academic disputation written in 1517 by the University of Wittenberg's moral theology professor, Martin Luther. The theses opposed the Catholic Church's practice of selling "indulgences" (certificates that were said to reduce the temporal punishment for sins committed by the purchasers or their loved ones in Purgatory), and it also claimed that salvation had to be achieved through personal repentance instead of through external sacramental confession. The theses were published on 31 October 1517, with the theses being nailed to the door of the All-Saints Church in Wittenberg for public display. The theses' publication led to Luther's excommunication in 1521 at the Diet of Worms, and their tenets would become the founding principles of Lutheran Protestantism.