The Eastern Orthodox Church, officially the Orthodox Catholic Church, and also called the Greek Orthodox Church or simply the Orthodox Church, is the second-largest Christian church, with approximately 230 million baptised members. It operates as a communion of autocephalous churches, each governed by its bishops via local synods. The church has no central doctrinal or governmental authority analogous to the head of the Catholic Church. Nevertheless, the Ecumenical Patriarch of Constantinople is recognised by them as primus inter pares, a title formerly given to the patriarch of Rome. As one of the oldest surviving religious institutions in the world, the Eastern Orthodox Church has played an especially prominent role in the history and culture of Eastern and Southeastern Europe.

The pope, also known as the supreme pontiff, Roman pontiff or sovereign pontiff, is the bishop of Rome, visible head of the worldwide Catholic Church, and has also served as the head of state or sovereign of the Papal States and later the Vatican City State since the eighth century. From a Catholic viewpoint, the primacy of the bishop of Rome is largely derived from his role as the apostolic successor to Saint Peter, to whom primacy was conferred by Jesus, who gave Peter the Keys of Heaven and the powers of "binding and loosing", naming him as the "rock" upon which the Church would be built. The current pope is Francis, who was elected on 13 March 2013.