The Reformation was initiated by Martin Luther in 1517 when he famously published his Ninety-Five Theses, which criticized the Catholic Church's practices, particularly the sale of indulgences. Luther's actions sparked a movement aimed at reforming the Church and addressing issues of doctrine and practice that he believed strayed from biblical teachings. His calls for reform resonated widely, leading to major religious, political, and cultural upheavals across Europe. The Reformation ultimately resulted in the establishment of Protestant denominations and significant changes within the Catholic Church.