Martin Luther's Ninety-five Theses were a list of 95 statements he wrote in 1517 that criticized certain practices of the Catholic Church, particularly the sale of indulgences. Indulgences were certificates that were sold by the Catholic Church that promised that the purchaser would be forgiven for their sins. Luther argued that indulgences were not biblical and that they undermined the grace of God.
Luther's Ninety-five Theses sparked the Protestant Reformation, which led to the split of the Christian church into various Protestant denominations and the Catholic Church.