Prior to and during the 16th century, the Church engaged in a process of reform and renewal. Reform during the 16th century is known as the Counter-Reformation.[1] In subsequent centuries, Catholicism spread widely across the world despite experiencing a reduction in its hold on European populations due to the growth of Protestantism and also because of religious skepticism during and after the Enlightenment. The Second Vatican Council in the 1960s introduced the most significant changes to Catholic practices since the Council of Trent four centuries before.