Eastern Orthodox Church

The Eastern Orthodox Church, which officially designates itself the Orthodox Catholic Church, traces its origins to the apostolic communities established in the early centuries of Christianity. Its principal ancient patriarchates — Constantinople, Alexandria, Antioch, and Jerusalem — maintained communion with the Church of Rome for centuries, experiencing only intermittent breaks such as the Photian schism and the Acacian schism. This shared communion persisted until the East–West Schism of 1054, which represented the culmination of mounting theological, political, and cultural disputes, most prominently concerning the authority of the pope. Before the Council of Ephesus in 431, the Church of the East also participated in this broader communion, as did the various Oriental Orthodox Churches before the Council of Chalcedon in 451, with those separations occurring primarily over Christological differences. The 1054 schism thus marked a decisive and enduring rupture between what would become the Roman Catholic and Eastern Orthodox traditions. Since 2018, an additional internal division has existed within Orthodoxy itself, with the patriarchates of Constantinople and Moscow no longer in full communion with each other.

The Eastern Orthodox Church understands itself as the one, holy, catholic, and apostolic Church established by Jesus Christ, maintaining that it preserves the original Christian faith through holy tradition. This tradition encompasses the Scriptures, the dogmatic decrees of the seven ecumenical councils, and the teachings of the Church Fathers. Eastern Orthodox theology holds that bishops are the successors of the apostles and that episcopal governance, exercised through local synods, is the proper structure of the Church. The church operates as a communion of autocephalous bodies, each self-governing, without a central doctrinal or governmental authority analogous to that of the pope in Roman Catholicism. The Ecumenical Patriarch of Constantinople is recognised within the communion as primus inter pares — first among equals — a designation that historically belonged to the patriarch of Rome before the schism. The Eastern Orthodox Church recognises seven major sacraments, which it calls holy mysteries, the chief of which is the Eucharist. The church teaches that through consecration invoked by a priest, the sacrificial bread and wine truly become the body and blood of Christ. The Virgin Mary holds a prominent place in Eastern Orthodox devotion, venerated under the title Theotokos, meaning 'God-bearer', and honoured through various liturgical and popular devotions.

From a Catholic perspective, the Eastern Orthodox Church occupies a singular place among Christian bodies separated from full communion with Rome. Unlike communities originating from the sixteenth-century Reformation, the Orthodox churches share with Catholicism an ancient common heritage: apostolic succession, a sacramental theology centred on the Eucharist, veneration of the Theotokos, and a deep patristic tradition. The East–West Schism of 1054 arose not from wholesale doctrinal innovation but from complex disputes over papal authority alongside cultural and political divergences, making the theological distance between Rome and Constantinople distinct in character from that between Catholicism and Protestant denominations. The Orthodox affirmation that the Eucharistic bread and wine become the body and blood of Christ through priestly consecration reflects a sacramental conviction shared with Catholic teaching. Similarly, the Orthodox veneration of Mary as Theotokos aligns with the title defined at the Council of Ephesus in 431, a council held before the later schisms. The ongoing division between Constantinople and Moscow since 2018 adds a further dimension to Catholic ecumenical engagement, as Rome must navigate relationships with a communion that is itself internally fractured.

The Eastern Orthodox Church remains the second-largest Christian body in the world, after the Roman Catholic Church, and constitutes the primary religious confession in numerous countries including Russia, Ukraine, Romania, Greece, Belarus, Serbia, Bulgaria, Georgia, Moldova, North Macedonia, Cyprus, and Montenegro. Eastern Orthodox Christians also form significant communities in Estonia, Bosnia and Herzegovina, Kosovo, Latvia, Syria, Lebanon, and other parts of the Middle East. Roughly half of all Eastern Orthodox Christians reside in the post-Eastern Bloc countries, the largest concentration being in Russia. The ancient communities in the former Byzantine regions of North Africa and the Eastern Mediterranean are among the oldest within Orthodoxy, though sources indicate these communities are decreasing due to forced migration driven by religious persecution. Outside Western Asia, Asia Minor, the Caucasus, and Eastern Europe, Orthodox communities in North America, Western Europe, and Australia have developed through diaspora migration, conversions, and missionary activity. The internal schism between Constantinople and Moscow, in place since 2018, continues to affect the coherence and external witness of the Orthodox communion.

The Eastern Orthodox Church has played an especially prominent role in the history and culture of Eastern and Southeastern Europe, functioning as one of the oldest surviving religious institutions in the world. Its patriarchates, descending from the ancient pentarchy model, include the historically significant sees of Constantinople, Alexandria, Antioch, and Jerusalem, each representing communities with roots extending to the apostolic era. The Ecumenical Patriarchate of Constantinople holds particular prominence, as its patriarch bears the title of primus inter pares within the Orthodox communion. The Russian Orthodox Church, centred in Moscow, represents by far the largest national Orthodox church in terms of population and geographic reach, and its current estrangement from Constantinople since 2018 marks a significant fracture in Orthodox ecclesial life. The churches of Greece, Romania, Serbia, and Bulgaria similarly represent major autocephalous bodies with deep historical and cultural ties to their respective nations. The Middle Eastern communities associated with the patriarchates of Antioch and Jerusalem preserve some of the earliest continuous traditions of Christian worship and witness.