For much of the written history of Christianity, episcopal government was the only known form of church organization. This changed at the Reformation. Many Protestant churches are now organized by either congregational or Presbyterian church polities, both descended from the writings of John Calvin.
Advocates for an Episcopal form of church government argue that the sheer fact that it went virtually uncontested until the time of the Reformation testifies to its claims of apostolicity.
Bishops considered their authority derived from an unbroken, personal apostolic succession from the Twelve Apostles of Jesus. Bishops with such authority are known as the historical episcopate. Churches with this type of government usually believe that the Church requires Episcopal government. In some systems, bishops may be subject to higher-ranking bishops.