Catholicism and Protestantism differ primarily in their views on religious authority, the nature of salvation, and practices like sacraments and the role of Mary and saints. Catholicism emphasizes both the Bible and Church Tradition as authoritative, while Protestantism generally holds that the Bible is the sole authority (Sola Scriptura). Protestants also emphasize salvation by faith alone through God's grace, while Catholicism includes the role of faith, good works, and sacraments.