Christianity has three main branches: Roman Catholicism, Eastern Orthodoxy, and Protestantism, which developed from the 16th Century Reformation. Protestantism has further branched into hun¬dreds of denominations arising from geographic, creedal, and organizational differences. Doctrines common to Protestantism include justification by faith through grace (salvation is the gift of God and cannot be earned), the priesthood of all believers (each person may approach God directly, with¬out any intermediary), and the authority of scriptures (the Bible is considered the ultimate guide for spiritual questions, though some traditions balance the Bible with other sources of understanding).

General forms of polity (church governance) include episcopal (authority centered in bishops), con¬gregational (each local group governs its own affairs with lay leadership equal to clergy), and pres¬byterian (regional groups of clergy and lay leaders governing certain matters for local congregations while relating to a national assembly).