The 95 Theses is a document written by Martin Luther in 1517 that challenged the practices of the Catholic Church, particularly the sale of indulgences. Luther argued that salvation could not be bought and that faith alone was the key to salvation. His theses sparked widespread debate and are often credited with initiating the Protestant Reformation. Luther posted the theses on the door of the Castle Church in Wittenberg, Germany, inviting discussion and reform. The document outlined 95 points of criticism against the Church's practices, emphasizing the need for a return to biblical teachings. This act marked a significant moment in religious history, leading to the formation of various Protestant denominations.