|Part of the series Orthodox Church|
|1||Meaning of Orthodox|
|3||Organization and leadership|
|4||Number of adherents|
|10||Relations with other christians|
|11||The church today|
The various autocephalous and autonomous synods of the Eastern Orthodox Church are distinct in terms of administration and local culture, but for the most part exist in full communion with one another. The Russian Orthodox Church Outside Russia (ROCOR) has recently united with the Moscow Patriarchate (MP); these two branches of the Russian Orthodox Church had separated from each other in the 1920s due to the subjection of the latter to the hostile Soviet regime (see Act of Canonical Communion).
Tensions exist in the philosophical differences between those who use the Revised Julian Calendar ("New Calendarists") for calculating the feasts of the ecclesiastical year and those who continue to use the traditional Julian Calendar ("Old Calendarists"). The calendar question reflects the dispute between those who wish to synchronize with the modern Gregorian calendar, which its opponents consider unnecessary and damaging to continuity, and those who wish to maintain the traditional ecclesiastical calendar (which happens to be based on the Julian calendar), emphasizing that such a major change in the tradition of the Church may only occur through the convening of an Ecumenical council. The dispute has led to much acrimony, and sometimes even to violence. Following canonical precepts, some adherents of the Old Calendar have chosen to abstain from clerical intercommunion with those synods which have embraced the New Calendar until the conflict is resolved. The monastic communities on Mount Athos have provided the strongest opposition to the New Calendar, and to modernism in general, while still maintaining communion with their mother church.
Some latent discontent between different national churches exists also in part due to different approach towards ecumenism. While the Ecumenical Patriarch of Constantinople, the Eastern Orthodox bishops in North America gathered into the Standing Conference of the Canonical Orthodox Bishops in the Americas (SCOBA), Romanian bishops, and others are fairly open to dialog with the Roman Catholic Church, both conservative and moderate Old Calendarists, many of the monks of Mount Athos, several bishops of Russian, Serbian, and some of Greek and Bulgarian churches regard ecumenism as compromising essential doctrinal stands in order to accommodate other Christians, and object to the emphasis on dialogue leading to inter-communion; believing instead that Orthodox must speak the truth with love, in the hope of leading to the eventual conversion to Eastern Orthodoxy of heterodox Christians.
Proponents of ecumenism are currently engaged in discussing key theological differences such as the Filioque, Papal primacy, and a possible agreement on rapprochement and eventually full communion with the Roman Catholic and Anglican Churches.
Eastern Orthodox churches in communion
The Eastern Orthodox Church is a communion of 14 autocephalous (that is, administratively completely independent) local churches plus the Orthodox Church in America which is recognized as autocephalous only by the Russian, Bulgarian, Georgian, Polish, and Czech-Slovak Churches. Each has defined geographical boundaries of its jurisdiction and is ruled by its Council of Bishops or Synod presided by a senior bishop – its Primate (or First Hierarch). The Primate may carry the honorary title of Patriarch, Metropolitan (in the Slavic tradition) or Archbishop (in the Greek tradition). Each local church consists of constituent eparchies (or, dioceses) ruled by a bishop. Some churches have given an eparchy or group of eparchies varying degrees of autonomy (self-government). Such autonomous churches maintain varying levels of dependence on their mother church, usually defined in a Tomos or other document of autonomy.
Below is a list of the 14 (15) autocephalous churches in their order of precedence (seniority) with constituent autonomous churches and exarchates. The Liturgical title of the Primate is listed in italics.
- Ecumenical Patriarchate of Constantinople  (Archbishop of Constantinople-New Rome and Ecumenical Patriarch)
- Autonomous Orthodox Church of Finland  (Archbishop of Karelia and All Finland)
- Autonomous Estonian Apostolic Orthodox Church  (Metropolitan of Tallinn and All Estonia) [Autonomy not recognized by the Church of Russia]
- Self-governing Orthodox Church of Crete (Archbishop of Crete)
- Self-governing Monastic Community of Mount Athos
- Exarchate of Patmos (Patriarchal Exarch of Patmos)
- Greek Orthodox Archdiocese of Thyateira and Great Britain  (Archbishop of Thyateira and Great Britain)
- Greek Orthodox Archdiocese of Italy and Malta  (Orthodox Archbishop of Italy and Malta and Exarch of Southern Europe)
- Greek Orthodox Archdiocese of America  (Archbishop of America)
- Greek Orthodox Archdiocese of Australia  (Archbishop of Australia)
- Exarchate of the Philippines  (Exarch of Philippines)
- Patriarchal Exarchate for Orthodox Parishes of Russian Tradition in Western Europe  (Archbishop of Komana)
- Orthodox Church of Alexandria  (Pope and Patriarch of the great city of Alexandria, Libya, Pentapolis, Ethiopia, all Egypt, and all Africa)
- Orthodox Church of Antioch  (Patriarch of Antioch and all the East)
- Self-governing Antiochian Orthodox Christian Archdiocese of North America  (Archbishop of New York and Metropolitan of All North America)
- Orthodox Church of Jerusalem  (Patriarch of the Holy City of Jerusalem and all Palestine, and of Syria, Arabia, beyond the Jordan River, Cana of Galilee, and Sacred Zion)
- Orthodox Church of Russia  (Patriarch of Moscow and all Russia)
- Autonomous Orthodox Church of Japan  (Archbishop of Tokyo and Metropolitan of All Japan)
- Autonomous Orthodox Church of China (defunct)
- Autonomous Orthodox Church of Ukraine  (Metropolitan of Kiev and all Ukraine)
- Self-governing Orthodox Church of Moldova  (Metropolitan of Chisinau and all Moldova)
- Self-governing Orthodox Church of Latvia  (Metropolitan of Riga and all Latvia)
- Self-governing Estonian Orthodox Church  (Metropolitan of Tallinn and all Estonia) [Autonomy not recognized by the Ecumenical Patriarchate]
- Self-governing Russian Orthodox Church Outside Russia  (Metropolitan of Eastern America and New York, First Hierarch of the Russian church abroad)
- Exarchate of Belarus (Metropolitan of Minsk and Slutsk, Patriarchal Exarch of All Belarus)
- Orthodox Church of Serbia  (Archbishop of Peć, Metropolitan of Belgrade and Karlovci, Patriarch of the Serbs)
- Orthodox Church of Romania  (Archbishop of Bucharest, Metropolitan of Ungro-Valachia, and Patriarch of All Romania)
- Orthodox Church of Bulgaria  (Metropolitan of Sofia and Patriarch of All Bulgaria)
- Orthodox Church of Georgia  (Archbishop of Tbilisi and Mshketi, Patriarch and Catholicos of all Georgia)
- Orthodox Church of Cyprus  (Archbishop of New Justiniana and all Cyprus)
- Orthodox Church of Greece  (Archbishop of Athens and all Greece)
- Orthodox Church of Poland  (Metropolitan of Warsaw and all Poland)
- Orthodox Church of Albania  (Archbishop of Tirana and all Albania)
- Orthodox Church of the Czech lands and Slovakia   (Archbishop of Prague, the Metropolitan of Czech lands and Slovakia or the Archbishop of Presov, the Metropolitan of Czech lands and Slovakia)
Some Orthodox do not acknowledge the following Church as autonomous & autocephalous:
- Orthodox Church in America  (Archbishop of Washington and New York, Metropolitan of all America and Canada) [Autonomy not recognized by the Ecumenical Patriarchate and most churches of the Eastern communion]
Note, that the Russian Church recognized a different order of seniority, in which the Georgian church comes after the Church of Russia and the Albanian Church – after the Church of Greece.
Eastern Orthodox Churches and communities not in communion with others
The following is list of some of the organizations that use the term "Orthodox" in their name but do not maintain communion with any of the 14 (15) autocephalous churches and thus are not typically considered part of the Eastern Orthodox Christian communion.
Old Calendarists are groups that do not maintain communion with the 14 (15) autocephalous churches as a result of the use of the Revised Julian Calendar.
- Church of the Genuine Orthodox Christians of Greece, so-called "Matthewites"
- Church of the Genuine Orthodox Christians of Greece, so-called "Florinites"
- Orthodox Church of Greece (Holy Synod in Resistance) , so-called "Cyprianites"
- Old Calendar Romanian Orthodox Church 
- Old Calendar Bulgarian Orthodox Church 
- Russian Orthodox Church in America 
Old Believers are groups that do not accept liturgical reforms carried out in the Russian Orthodox Church by Patriarch Nikon in the 17th century.
- Russian Orthodox Old-Rite Church  (Belokrinitskaya Hierarchy)
- Lipovan Orthodox Old-Rite Church (Belokrinitskaya Hierarchy)
- Russian Old-Orthodox Church (Novozybkovskaya Hierarchy)
- Pomorian Old-Orthodox Church (Pomortsy)
Episcopi vagantes are entities that have carried out episcopal consecrations outside of the norms of canon law or whose bishops have been excommunicated by one of the 14 (15) autocephalous churches.
- Belarusian Autocephalous Orthodox Church
- Bulgarian Alternative Synod
- Holy Orthodox Church in North America
- Macedonian Orthodox Church 
- Montenegrin Orthodox Church 
- Orthodox Church in Italy 
- Russian True Orthodox Church 
- Turkish Orthodox Church
- Ukrainian Orthodox Church (Kiev Patriarchate) 
- Ukrainian Autocephalous Orthodox Church 
- Ukrainian Autocephalous Orthodox Church Canonical