The Armenian Apostolic Church, sometimes called the Armenian Orthodox Church is one of the original churches, having separated from the then-still-united Roman Catholic/Byzantine Orthodox church in 506, after the Council of Chalcedon (see Oriental Orthodoxy). The Armenian church has been labeled monophysite because they rejected the decisions of this council, which condemned monophysitism. The Coptic Orthodox Church also separated after the Council of Chalcedon. The Armenian church does not hold to monophysite doctrine, however, but confesses the two natures of Christ. The Armenian church also rejects the juridical authority of the pope and the doctrine of purgatory.
The head of the Armenian Apostolic Church is the Catholicos of Armenia (the plural is Catholicoi). (The Armenian Apostolic Church should not be confused, however, with the Armenian Catholic Church, which is an Eastern Rite church under the authority of the Pope in Rome.) At present, the Catholicos of Armenia is Garegin II, who resides in the city of Echmiadzin, west of Yerevan. However, a minority of the church has recognized instead the Catholicos of Cilicia, who resides in Antilyas in Lebanon, as a result of a dispute that emerged while Armenia was under Communist rule.
Liturgically, the Church has much more in common with the Latin rite, especially as it was at the time of separation, than other Orthodox rites. For example, their bishops wear vestments almost identical to those of Western bishops. They usually do not use a full iconostasis, but rather a curtain (which was also used in the West at the time of separation).
Armenia was the first country to adopt Christianity as its official religion, in AD 301, when Saint Gregory the Illuminator converted the king of Armenia, Trdat IV, to Christianity.
Today there are large Armenian Orthodox congreations in many middle-eastern countries outside Iran (see also Christians in Iran) where Armenians are the largest Christian ethnic minority.
Other large Armenian Orthodox congregations are in the USA and in many Western European countries.