The Protestant Reformation began in the 16th century as a religious reform movement that divided Western Christianity into Catholic and Protestant branches. Martin Luther, a German monk and theology professor, nailed his 95 Theses criticizing Catholic Church practices like indulgences to a church door in 1517. This sparked the Reformation. Luther questioned Church doctrine on salvation and advocated faith alone rather than faith plus good works. He was excommunicated in 1521 but his ideas spread rapidly with the help of the printing press. The Reformation divided Europe and led to new Protestant movements like Calvinism and Anabaptism, while the Catholic Church launched its own reforms through figures like Ignatius of Loyola and councils like Trent.