Ninety-Five Theses was written by Martin Luther in 1517 and is widely regarded as the primary catalyst for the Protestant Reformation. The disputation protests against clerical abuses, especially the sale of indulgences.
In 1516, a Dominican friar named Johann Tetzel came through Germany, selling indulgences to raise money for the Archbishop of Mainz, who needed to pay the pope for his appointment.
Luther was outraged because these indulgences appeared to say that the people holding them had purchased their salvation. In response to the indulgence sale, he wrote the 95 Theses, attacking the practice, affirming that salvation and forgiveness are free gifts from God, and inviting a public debate on the subject at his university.
On October 31, 1517, he nailed a copy of the 95 Theses to the door of the Schlosskirche (Castle Church) at Wittenberg, an event later mythologized as the start of the Protestant Reformation.