The Protestant Reformation dates to Martin Luther's publication of his "95 Theses" in 1517. Luther, an Augustinian monk, continued publishing tracts and pamphlets calling for a purification of the Catholic Church and Christian adherence to the Bible.
For years, Luther had been critical of the Catholic Church, particularly of the idea of selling indulgences, or reprieves from penance. Luther had been disillusioned by what he saw as the Church's corruption, especially as manifested in the Pope's matter-of-fact selling of indulgences. Deeply religious, he had studied the problem and prayed for years to determine what he might do.
In 1517, Luther became infuriated when Pope Leo X announced a fresh sale of indulgences to help pay for the construction of St. Peter's Basilica. In this passionate mood, he wrote the "95 Theses," a devastating critique of what indulgences were doing to Christian faith and attitude, and nailed a copy to the University of Wittenberg's chapel door. Printed copies spread throughout Germany within two weeks, throughout the rest of Europe within two months. Strengthened in the belief that he was right, Luther continued writing and publishing tracts increasingly critical of the Catholic Church.
In 1521, Luther was summoned to the Diet of Worms, where he was excommunicated and declared a convicted heretic, putting him at risk of execution. Nevertheless, Friedrich III, Elector of Saxony, shielded Luther so that he might continue teaching and, eventually, found Lutheranism.