The Eastern Orthodox Church, officially the Orthodox Catholic Church,[2][3][4][5] is the secondlargest Christian church, with approximately 260 million baptised members.[1][6][7][8][9] It operates as
a communion of autocephalous churches, each governed by its bishops in local synods.[8]Roughly
half of Eastern Orthodox Christians live in Russia. The church has no central doctrinal or
governmental authority analogous to the Bishop of Rome, but the Ecumenical Patriarch of
Constantinople is recognised by all as primus inter pares ("first among equals") of the bishops. As
one of the oldest surviving religious institutions in the world, the Eastern Orthodox Church has
played a prominent role in the history and culture of Eastern and Southeastern Europe,
the Caucasus, and the Near East.[10]
Eastern Orthodox theology is based on the Nicene-Constantinopolitan Creed (known simply as the
Nicene Creed). The church teaches that it is the One, Holy, Catholic and
Apostolic church established by Jesus Christ in his Great Commission, and that its bishops are
the successors of Christ's apostles.[11] It maintains that it practices the original Christian faith, as
passed down by holy tradition. Its patriarchates, reminiscent of the pentarchy,
and autocephalous and autonomous churches reflect a variety of hierarchical organisation. Of its
innumerable[clarification needed] sacred mysteries, it recognises seven major sacraments, of which
the Eucharist is the principal one, celebrated liturgically in synaxis. The church teaches that
through consecration invoked by a priest, the sacrificial bread and wine become the body and blood
of Christ. The Virgin Mary is venerated in the Eastern Orthodox Church as the God-bearer,
honoured in devotions.
The Eastern Orthodox Church shared communion with the Roman Catholic Church until the East–
West Schism in 1054, disputing particularly the authority of the Pope. Before the Council of
Ephesus in AD 431 the Church of the East also shared in this communion, as did the Oriental
Orthodox churches before the Council of Chalcedon in AD 451, all separating primarily
over differences in Christology.
The majority of Eastern Orthodox Christians live mainly in Southeast and Eastern
Europe, Cyprus, Georgia and other communities in the Caucasus region, and communities
in Siberia reaching the Russian Far East. There are also smaller communities in the
former Byzantine regionsof Africa, the Eastern Mediterranean, and in the Middle East where it is
decreasing due to forced migration because of increased religious persecution in recent
years.[12][13] There are also many in other parts of the world, formed through diaspora, conversions,
and missionary activity.