The Eastern Orthodox Church is a communion comprising the fourteen or sixteen separate autocephalous (self-governing) hierarchical churches that recognize each other as "canonical" Eastern Orthodox Christian churches.
Each constituent church is self-governing; its highest-ranking bishop called the primate (a patriarch, a metropolitan or an archbishop) reports to no higher earthly authority. Each regional church is composed of constituent eparchies (or dioceses) ruled by bishops. Some autocephalous churches have given an eparchy or group of eparchies varying degrees of autonomy (limited self-government). Such autonomous churches maintain varying levels of dependence on their mother church, usually defined in a Tomos or other document of autonomy. In many cases, autonomous churches are almost completely self-governing, with the mother church retaining only the right to appoint the highest-ranking bishop (often an archbishop or metropolitan) of the autonomous church.
Normal governance is enacted through a synod of bishops within each church. In case of issues that go beyond the scope of a single church, multiple self-governing churches send representatives to a wider synod, sometimes wide enough to be called an Eastern Orthodox "ecumenical council". Such councils are deemed to have authority superior to that of any autocephalous church or its ranking bishop.
The Orthodox Church is decentralised, having no central authority, earthly head or a single Bishop in a leadership role. Thus, the Orthodox Church uses a synodical system canonically, which is significantly different from the hierarchically organised Catholic Church that follows the doctrine of papal supremacy. References to the Ecumenical Patriarch of Constantinople as a leader are an erroneous interpretation of his title ("first among equals"). His title is of honor rather than authority and in fact the Ecumenical Patriarch has no real authority over Churches other than the Constantinopolitan. His unique role often sees the Ecumenical Patriarch referred to as the "spiritual leader" of the Eastern Orthodox Church in some sources.
The autocephalous churches are normally in full communion with each other, so any priest of any of those churches may lawfully minister to any member of any of them, and no member of any is excluded from any form of worship in any of the others, including reception of the Eucharist.
In the early Middle Ages, the early Christian church was ruled by five patriarchs as the state church of Rome: the bishops of Rome, Constantinople, Alexandria, Antioch, and Jerusalem; these were collectively referred to as the Pentarchy. Each patriarch had jurisdiction over bishops in a specified geographic region. This continued until 927, when the autonomous Bulgarian Archbishopric became the first newly promoted patriarchate to join the original five.
The patriarch of Rome was "first in place of honor" among the five patriarchs. Disagreement about the limits of his authority was one of the causes of the Great Schism, conventionally dated to the year 1054, which split the church into the Catholic Church in the West, headed by the Bishop of Rome, and the Orthodox Church, led by the four eastern patriarchs (Constantinople, Jerusalem, Antioch and Alexandria). After the schism this honorary primacy shifted to the Patriarch of Constantinople, who had previously been accorded the second-place rank at the First Council of Constantinople.
In the 5th century, Oriental Orthodoxy separated from Chalcedonian Christianity (and is therefore separate from both the Eastern Orthodox and Catholic Church), well before the 11th century Great Schism. It should not be confused with Eastern Orthodoxy.
Ranked in order of seniority, with the year of independence (autocephaly) given in parentheses, where applicable. There is a total of 16 autocephalous Eastern Orthodox churches which are recognized.
Those four ancient Eastern Orthodox Patriarchates are of the five episcopal sees forming the historical Pentarchy, the fifth one being the See of Rome. They all adopted the Chalcedonian Definition and remained in communion after the schism that followed the Council of Chalcedon in 451. The council was the fourth of the Ecumenical Councils that are accepted by Chalcedonian churches which include the Eastern Orthodox, and also the Catholic, and most Protestant churches. It was the first council not to be recognised by any Oriental Orthodox churches (classified as non-Chalcedonian).
The four ancient patriarchates are the most senior, followed by the five junior patriarchates. Autocephalous archbishoprics follow the patriarchates in seniority, with the Church of Cyprus being the only ancient one (AD 431). In the diptychs of the Russian Orthodox Church and some of its daughter churches (e.g., the Orthodox Church in America), the ranking of the five junior patriarchal churches is different. Following the Russian Church in rank is Georgian, followed by Serbian, Romanian, and then Bulgarian Church. The ranking of the archbishoprics is the same.
These are churches that have separated from the mainstream communion over issues of Ecumenism and Calendar reform since the 1920s. Due to what these churches perceive as being errors of modernism and the branch theory (which they call "ecumenism") in mainstream Eastern Orthodoxy, they refrain from concelebration of the Divine Liturgy with the mainstream Eastern Orthodox, while maintaining that they remain fully within the canonical boundaries of the Church: i.e., professing Eastern Orthodox belief, retaining legitimate apostolic succession, and existing in communities with historical continuity.
The Churches which follow True Orthodoxy are:
These Churches do not practice Communion with any other Eastern Orthodox jurisdictions nor do they tend to recognize each other. Yet, like the True Orthodox Churches above, they consider themselves to be within the canonical boundaries of the Church: i.e., professing Eastern Orthodox belief, retaining what they believe to be legitimate apostolic succession, and existing in communities with historical continuity. Nevertheless, their relationship with all other Eastern Orthodox Churches remains unclear, as Eastern Orthodox Churches normally recognize and are recognized by others.
Old Believers are divided into various churches which do not recognize each others, nor mainstream Eastern Orthodox Churches.
The following Churches recognize all other mainstream Eastern Orthodox Churches, but are not recognized by any of them due to various disputes:
The following Churches use the term "Orthodox" in their name and carries belief or the traditions of Eastern Orthodox church, but blend beliefs and traditions from other denominations outside of Eastern Orthodoxy: