The Oriental Orthodox churches are among the oldest Christian churches in existence, and the term reflects one of the earliest schisms within Christianity. The Oriental Orthodox Church and the rest of the Christian church, centered in Rome, broke apart during the 5th century CE. They are sometimes also called "non-Chalcedonian churches", as the schism that separates them from Roman Catholics and Eastern Orthodox Christians began in the wake of the fourth ecumenical council, the Council of Chalcedon.

Don't confuse Oriental Orthodox Christianity with Eastern Orthodox Christianity; the names are similar, and both can be categorized under Eastern Christianity. But the separation between the Eastern Orthodox Church and the Roman Catholic Church occurred later, during the Great Schism of the 11th century. The division between the Oriental Orthodox churches and the rest of the Christian Church is much older. Furthermore, don't confuse the Oriental Orthodox Church with the Assyrian Church of the East (sometimes, and confusingly, called the Assyrian Orthodox Church), which entered schism with the rest of the Christian Church some years before the Catholic-Oriental Orthodox schism, and whose beliefs are roundly denounced by the Oriental Orthodox Church.

Organization

Much like the Eastern Orthodox Church, the Oriental Orthodox Church is organized as a collection of several autocephalous churches, which are in full communion with one another but whose highest ranking bishops do not report to a higher authority in the church's hierarchy.

• Armenian Apostolic Church

The Armenian church was founded in 301, and is the oldest national church in the world. Christianity was carried to Armenia by two Apostles, Saint Bartholomew and Saint Thaddeus. The head of the Armenian Apostolic Church is called a catholicos (pl. catholicoi); at the time of this writing, the catholicos is His Holiness Karekin II. The liturgy of the Armenian Apostolic Church resembles the Latin Rite of the Roman Catholic Church; outside Armenia, members are found in the United States, France, Lebanon, Russia, Syria, and Iran.

• Coptic Orthodox Church

The Coptic church draws back, according to tradition, to the church established by Saint Mark in Egypt in the mid 1st century. Its leader is the Pope of Alexandria; at the time of writing, it is Shenouda III. Coptic Christianity has a strong monastic movement, owing to the establishment of monasteries established by Christians fleeing persecution in the 3rd century. Some liturgical use still exists of the Coptic language (which evolved from the ancient Egyptian language), though most preaching today is in Arabic.

• Ethiopian Orthodox Church

The Ethiopian Orthodox Church was granted its own patriarch, the Patriarch of Ethiopia in 1959, which made it separate from the Coptic church (although still in full communion with the Coptic church and the rest of the Oriental Orthodox churches.) According to tradition, it was founded by Philip the Evangelist. Its current patriarch (at the time of this writing) is Abune Paulos. However, the previous patriarch, Abune Merkorios, who officially abdicated the throne, claims that his abdication was under duress from Ethiopia's ruling regime, and maintains a synod in exile in the United States.

• Eritrean Orthodox Church

Upon the independence of Eritrea from Ethiopia in 1993, the Eritrean church petitioned the Coptic pope for its own patriarch and thus autocephaly. Recently (as of the time of this writing), news has come out of Eritrea that the nation's government has forced the current Patriarch of Eritrea, Abune Antonios, out of office. This is clearly not legitimate according to the laws of the church.

• Malankara Orthodox Church (Indian Orthodox Church)

According to tradition, the Malankara Orthodox Church was founded in 52 CE by the apostle Saint Thomas. Its rituals are Indian in style, with liturgies in Hindi, Malayalam, and English. The leader of the church is the Catholicos of the East, whose office is in Kottayam, in Kerala. The current Catholicos, at the time of this writing, is Baselius Mar Thoma Mathews II.

• Syriac Orthodox Church

The Syriac Orthodox Church is led by the Patriarch of Antioch, who resides nowadays in Damascus. At the time of this writing, the Syriac patriarch is His Holiness Mor Ignatius Zakka I Iwas. Tradition holds that it was founded by the apostle Saint Peter in 34 CE, and is the oldest Christian church, although the Antiochian Orthodox Church, part of the Eastern Orthodox Communion, also claims to be the legitimate Church of Antioch.

Each of these individual churches is organized hierarchically, under a patriarch (known by additional titles in some of the churches, with the Coptic Patriarch titled Pope) who holds authority over the church's membership. As with the Roman Catholic Church, the Oriental Orthodox churches have three degrees of Holy Orders: bishop, priest, and deacon. The style of church government shared by the Roman Catholic, Eastern Orthodox, Oriental Orthodox, and Anglican churches is known as episcopalian governance, with the authority originally held by the Apostles now vested in the bishops (to be discussed below.) Both the Eastern Orthodox and Oriental Orthodox churches lack a single, preeminent leader; the patriarchs of these churches are understood to be the next step down the hierarchy, with Jesus as the Christian Church's only leader (though whether He leads the Eastern Orthodox or Oriental Orthodox Church will be left as an exercise for the reader.)

History

The schism between the rest of the Christian Church and the Oriental Orthodox Church occured after the fourth ecumenical council in 451; that Council and all of the ones that followed are repudiated by the Oriental Orthodox Church. The root of the disagreement lies - as with many disagreements in the early Christian Church - with the conception of Christ's nature as a combination of the human and the divine.

The organization of the early Christian Church

The Christian Church of the first few centuries CE (called in the Nicene Creed the One Holy Catholic and Apostolic Church) was lead by five patriarchs, who sat in Rome, Constantinople, Jerusalem, Antioch, and Alexandria. They each had supreme authority over their own territory, but there was no supreme figure - the patriarchs met as equals, though the Roman patriarch, the Patriarch of the West was "first among equals," a position that came without any formal powers over the other patriarchs. His preeminent status was due to his succeeding Saint Peter, whom Jesus declared to be the first leader of the Christian Church. Rome thus became the political center of Christendom.

With the fragmentation of the Roman Empire into eastern and western halves, and the eventual destruction of the Western Roman Empire, Rome lost its political importance and gradually the West fell into chaos. The Eastern Roman Empire, which became the Byzantine Empire, centered in Constantinople, continued to flourish. The lingua franca of the West was Latin, while that of the East was Greek, and while these cultural differences were minor and had been easily bridged in earlier years, the cultural split between East and West grew over time and was eventually to become a political split as well.

The first three ecumenical councils

The ecumenical councils were meetings of the bishops of the entire Christian Church, beginning in 325 with the Council of Nicea. During these meetings, matters of doctrine and church practice were established by discussion and voting amongst the bishops. The Council of Nicea established the fundamentals of Christian faith, including the trinity, the Nicene Creed, and the nature of Jesus as an equal, uncreated part of the Godhead (thus repudiating the doctrine of Arianism, which held Jesus to be created by the Father.) The few non-trinitarian Christian churches do not accept the validity of the Council of Nicea or any of the subsequent ecumenical councils.

The second ecumenical council, the First Council of Constantinople, dealt mostly with the nature of the Holy Spirit. It took place in 381 and established that the Holy Spirit is of the same substance as the Father, thus repudiating the heresy that the Holy Spirit was not divine. The third council, the Council of Ephesus of 431, dealt with Nestorianism, the heresy that Jesus' human and divine natures were separate, although it's difficult to determine exactly what Nestorius preached, as much of the controversy was probably due to semantics and exaggerations or misstatements of the opposing parties' views. Nevertheless, the Christian Church was split apart by the argument, resulting in the first schism in the Church and the separation of the Assyrian Church of the East (again, not to be confused with any of the Oriental Orthodox churches) from the rest of Christianity.

The monophysite heresy

With the fourth ecumenical council, the Council of Chalcedon in 451, the Church addressed monophysitism, the belief that Christ has only one single nature. Monophysites believe either that Jesus had a human body but a divine mind (more or less), or that the human nature of Jesus "dissolved like a drop of honey in the sea" due to the force of his divine nature. Monophysitism developed essentially out of opposition to Nestorianism, and it was condemned as heretical by the Council of Chalcedon.

The argument amongst the bishops was intense; in the aftermath of the council, some bishops repudiated its findings, claiming that the belief that Christ had two natures was tantamount to Nestorianism; these bishops, in turn, were declared to be monophysite by the rest of the Church, though they denied it. The disagreement led to another schism, this time between the bishops who accepted the validity of the Council of Chalcedon and those who didn't. The Roman Church and the Oriental Orthodox Church were established as separate bodies, each maintaining that it was the One True Church.

It's important to note that Oriental Orthodox doctrine is properly regarded not as monophysite, but "miaphysite", which holds that Christ's divinity and humanity are united in a single nature. In truth, this view is essentially the same as that of the Roman Catholic or Eastern Orthodox churches, but again subtle semantic issues proved divisive to the early Christian Church.

Since then

Some Oriental Orthodox churches have broken from the Oriental Orthodox communion and entered the Roman Catholic Communion. These churches, which are among the Eastern Rite Catholic churches, are organized much like the Oriental Orthodox churches, headed by patriarchs who have some degree of indepedence from Rome. The Eastern Rite churches have different liturgical rituals than the main body of the Roman Catholic Church, and they have slightly different practices - priests, for instance, are not required to remain celibate in Eastern Rite churches.

The Oriental Orthodox Communion and the Roman Catholic Communion have established closer ties during the 20th century. Recognition has grown that the theological separation between the two churches is small or even nonexistent. In 1984, Pope John Paul II and His Holiness Mar Ignatius Zakka I Iwas, the Patriarch of Antioch and head of the Syriac Orthodox Church, released a joint statement that included the words, "The confusions and schisms that occurred between their Churches in the later centuries, they realize today, in no way affect or touch the substance of their faith, since these arose only because of differences in terminology and culture and in the various formulae adopted by different theological schools to express the same matter. . . . Accordingly, we find today no real basis for the sad divisions and schisms that subsequently arose between us concerning the doctrine of Incarnation." Their statement established mutual recognition of each other's sacraments; the rapprochement between the churches may be a sign of a future movement towards full communion between the two bodies.

Apostolic succession

Apostolic succession refers to the Christian doctrine that the Apostles, during the time of Jesus, were divinely granted the authority to perform certain rites, like blessing the Eucharist during Holy Communion. This authority can be transmitted to another through the rite of ordination, and (according to those denominations that subscribe to the doctrine), there is an unbroken line of transmission of this authority from the Apostles to their modern-day successors, the bishops.

The Roman Catholic Church, the Church of England, the Eastern Orthodox Church, and the Oriental Orthodox Church, along with a few Protestant denominations and (in a radically altered form) the Mormon Church all share the doctrine of apostolic succession. The Roman Catholic Church indeed recognizes the validity of sacraments performed by priests of both of the Orthodox churches.

The relevance of this is that, like the Roman Catholic and Eastern Orthodox churches, the Oriental Orthodox Church extends in an unbroken line from the early Christian church, which according to these churches' beliefs, was specially created and endowed by Jesus. "And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it." (Matthew 16:18)

Sources

http://www.prounione.urbe.it/dia-int/oo-rc_syrindia/doc/i_oo-rc_syrindia_1984.html
http://www.wcc-coe.org/wcc/what/ecumenical/ooc-e.html
http://www.orthodoxinfo.com/ecumenism/east_orth.aspx
http://www.bible.ca/orthodox-church-autocephalous-hierarchy-organization.htm
http://www.ecumenism.net/denom/orthodox.htm
http://www.sain.org/Armenian.Church/intro.txt
http://www.wcc-coe.org/wcc/what/ecumenical/o-e.html