Eastern Christianity comprises Christian traditions and church families that originally developed during classical and late antiquity in Western Asia, Asia Minor, Eastern Europe, Southeastern Europe, the Caucasus, Northeast Africa, the Fertile Crescent and the Malabar coast of South Asia, and ephemerally parts of Persia, Central Asia and the Far East. The term does not describe a single communion or religious denomination.
Major Eastern Christian bodies include the Eastern Orthodox Church and the Oriental Orthodox Churches, along with those groups descended from the historic Church of the East (aka the Assyrian Church), as well as the Eastern Catholic Churches (which have either re-established or always retained communion with Rome and maintain Eastern liturgies), and the Eastern Protestant churches (which are Protestant in theology but Eastern in cultural practice). The various Eastern churches do not normally refer to themselves as "Eastern", with the exception of the Assyrian Church of the East and its offshoot, the Ancient Church of the East.
The Eastern Orthodox are the largest body within Eastern Christianity with a worldwide population of 220 million, followed by the Oriental Orthodox at 60 million. The Eastern Catholic Churches consist of about 16–18 million and are a small minority within the Catholic Church. Eastern Protestant Christian churches do not form a single communion; churches like the Ukrainian Lutheran Church and Mar Thoma Syrian Church have under a million members. The Assyrian Church of the East and the Ancient Church of the East, descendant churches of the Assyria based Church of the East, have a combined membership of approximately 400,000, with other Assyrians being Catholics within the Chaldean Catholic Church which broke away from the Assyrian Church in the late 17th Century.
Historically, after the loss of the Levant in the 7th century to the Islamic Sunni Caliphate, the term Eastern Church was used for the Greek Church centered in Byzantium, in contrast with the (Western) Latin Church, centered on Rome, which uses the Latin liturgical rites.