A united church, also called a uniting church, is a denomination formed from the merger or other form of church union of two or more different Protestant Christian denominations, a number of which come from separate and distinct denominational orientations or traditions. Multi-denominationalism, or a multi-denominational church or organization, is a congregation or organization that is affiliated with two or more Christian denominations, whether they be part of the same tradition or from separate and distinct traditions.
Historically, unions of Protestant churches were enforced by the state, usually in order to have a stricter control over the religious sphere of its people, but also for other organizational reasons. As modern Christian ecumenism progresses, unions between various Protestant traditions are becoming more and more common, resulting in a growing number of united and uniting churches. Examples include the United Church of Canada (1925), the Church of South India (1947), the United Methodist Church (1968), the Uniting Church in Australia (1977), the Protestant Church in the Netherlands (2004), and the United Protestant Church of France (2013).