The event that signaled the start of the Reformation in Germany was Martin Luther's posting of the Ninety-Five Theses in 1517. These theses challenged the practices of the Catholic Church, particularly the sale of indulgences, and called for a return to biblical teachings. By articulating his critiques and advocating for reform, Luther ignited widespread debate and dissent within Christendom. This act is often viewed as a catalyst for the Protestant Reformation, leading to significant theological debates and the eventual establishment of various Protestant denominations. Luther’s actions significantly altered the religious landscape of Europe and had lasting implications for Christianity.