Oriental Orthodoxy, also known by several other names, is a Christian denomination in Eastern Christianity which recognizes only the first three ecumenical councils – the First Council of Nicaea in 325, the First Council of Constantinople in 381 and the Council of Ephesus in 431.
Oriental Orthodoxy is a communion of six (self-governing) Churches: the Coptic Orthodox Church of Alexandria, the Ethiopian Orthodox Tewahedo Church, the Eritrean Orthodox Tewahedo Church, the Syriac Orthodox Church, the Armenian Apostolic Church and the Malankara Orthodox Syrian Church. Oriental Orthodoxy has approximately 84 million adherents worldwide.
Oriental Orthodox Churches each uphold their own ancient ecclesiastic traditions of apostolic succession and catholicity (universal doctrine). These Churches rejected the definition of the two natures of Christ (human and divine), known as the Chalcedonian Definition, from the fourth ecumenical council, the Council of Chalcedon in 451. One-by-one, they discontinued their communion with the Great Church and developed separate institutions that did not participate in any of the later ecumenical councils.
By 1054, the East–West Schism resulted in the Great Church further splitting into bodies that are today known as the Roman Catholic Church and the Eastern Orthodox Church based on other Christological differences. The Eastern Orthodox maintain numerous theological and ecclesiological similarities with the Oriental Orthodox, but continue to disagree over the Chalcedonian Definition. The Oriental Orthodox Churches are in full communion with each other, but not with the Eastern Orthodox Church, despite the similar name. Slow dialogue towards restoring communion between the two Orthodox groups began in the mid-20th century, and dialogue is also underway between Oriental Orthodoxy and the Roman Catholic Church and others.