Eastern Orthodox Church organization in the context of "Full communion"

The Eastern Orthodox Church, officially the Orthodox Catholic Church, and also called the Greek Orthodox Church or simply the Orthodox Church, is one of the three major doctrinal and jurisdictional groups of Christianity. As of 2012, it has approximately 300 million adherents and is the third largest religious community in the world after Catholics and Sunni Muslims. The Eastern Orthodox Church operates as a communion of autocephalous churches, each governed by its bishops via local synods. The church has no central doctrinal or governmental authority analogous to the pope of the Catholic Church. Nevertheless, the Ecumenical Patriarch of Constantinople is recognised by them as primus inter pares ('first among equals'), a title held by the patriarch of Rome prior to 1054. As one of the oldest surviving religious institutions in the world, the Eastern Orthodox Church has played an especially prominent role in the history and culture of Eastern and Southeastern Europe. Since 2018, there has been an ongoing schism between Constantinople and Moscow, with the two not in full communion with each other.

Eastern Orthodox theology is based on the Scriptures and holy tradition, which incorporates the dogmatic decrees of the seven ecumenical councils, and the teaching of the Church Fathers. The church teaches that it is the one, holy, catholic and apostolic church established by Jesus Christ in his Great Commission, and that its bishops are the successors of Christ's apostles. It maintains that it practises the original Christian faith, as passed down by holy tradition. Its patriarchates, descending from the pentarchy, and other autocephalous and autonomous churches, reflect a variety of hierarchical organisation. It recognises seven major sacraments (which are called holy mysteries), of which the Eucharist is the principal one, celebrated liturgically in synaxis. The church teaches that through consecration invoked by a priest, the sacrificial bread and wine become the body and blood of Christ. The Virgin Mary is venerated in the Eastern Orthodox Church as the Theotokos, which means 'God-bearer', and she is honoured in devotions.

The Greek Orthodox Patriarchate of Jerusalem, also known as the Greek Orthodox Church of Jerusalem, is an autocephalous church within the wider communion of Eastern Orthodox Christianity. Established in the mid-fifth century as one of the oldest patriarchates in Christendom, it is headquartered in the Church of the Holy Sepulchre in Jerusalem and led by the patriarch of Jerusalem, currently Theophilos III. The patriarchate's ecclesiastical jurisdiction includes roughly 200,000 to 500,000 Orthodox Christians across the Holy Land in Palestine, Jordan and Israel.

The church traces its foundation in Jerusalem to the day of Pentecost, when the Holy Spirit, according to Christian beliefs, descended on the disciples of Jesus Christ and ushered the spread of the Gospel. The church celebrates its liturgy in the ancient Byzantine Rite – whose sacred language, Koine Greek, is the original language of the New Testament – and follows its own liturgical year under the Julian calendar.

The 2018 Moscow–Constantinople schism is an ongoing schism between the Russian Orthodox Church (ROC, also known as the Moscow Patriarchate) and the Ecumenical Patriarchate of Constantinople, which began on 15 October 2018 when the former unilaterally severed full communion with the latter.

The resolution was taken in response to a decision of the Holy Synod of the Ecumenical Patriarchate of Constantinople of 11 October 2018, confirming its intentions to grant autocephaly to the Orthodox Church of Ukraine in the future. The decision also stated that the Holy Synod would immediately: reestablish a stauropegion in Kyiv, i.e. a church body subordinated directly to the ecumenical patriarch; revoke the "Letter of issue" (permission) of 1686 that had given permission to the patriarch of Moscow to ordain the metropolitan of Kiev and lift the excommunications which affected the clergy and faithfuls of two unrecognized Ukrainian Eastern Orthodox churches. Those two unrecognized churches, the Ukrainian Autocephalous Orthodox Church (UAOC) and the Ukrainian Orthodox Church – Kyiv Patriarchate (UOC-KP), were competing with the Ukrainian Orthodox Church (Moscow Patriarchate) (UOC-MP) and were considered "schismatics" (illegally segregated groups) by the Patriarchate of Moscow, as well as by the other Eastern Orthodox churches.

The Ukrainian Orthodox Church – Kyiv Patriarchate (UOC-KP; Ukrainian: Украї́нська Правосла́вна Це́рква – Ки́ївський Патріарха́т (УПЦ-КП), romanized: Ukrainska Pravoslavna Tserkva — Kyivskyi Patriarkhat (UPTs-KP)) was an Orthodox church in Ukraine, in existence from 1992 to 2018. Its patriarchal cathedral was St Volodymyr's Cathedral in Kyiv.

After its unilateral declaration of autocephaly in 1992, the UOC-KP was not recognised by the other Eastern Orthodox churches, and was considered a "schismatic group" by the Moscow Patriarchate and Ecumenical Patriarchate. Patriarch Filaret (Denysenko) was enthroned in 1995 and excommunicated by the Russian Orthodox Church in 1997, an action not recognized by the UOC-KP synod. In 2018, the Ecumenical Patriarchate of Constantinople moved unilaterally and against canonical norms to facilitate a "unification council", in contradiction to his previous statement "recognizing the fullness of the Russian Orthodox Church's exclusive competence on this issue". The canonical Ukrainian Orthodox Church rejected these overtures, noting its universal recognition as sole canonical authority on the territory of Ukraine and the political nature of the proposed council. Constantinople ignored this, "reinstated" Filaret as a bishop and facilitated the convening of a unification council. In December 2018, the unification council of the Eastern Orthodox churches of Ukraine decided to unite the UOC-KP with the Ukrainian Autocephalous Orthodox Church (UAOC), creating the Orthodox Church of Ukraine (OCU) which was subsequently granted autocephaly by the Ecumenical Patriarch of Constantinople in January 2019.

The Romanian Orthodox Church (ROC; Romanian: Biserica Ortodoxă Română, BOR), or Romanian Patriarchate, is an autocephalous Eastern Orthodox church in full communion with other Eastern Orthodox Christian churches, and is one of the nine patriarchates in the Eastern Orthodox Church. Since 1925, the church's Primate has borne the title of Patriarch. Its jurisdiction covers the territories of Romania and Moldova, with additional dioceses for Romanians living in nearby Ukraine, Serbia and Hungary, as well as for diaspora communities in Central and Western Europe, North America and Oceania. It is the only autocephalous church within Eastern Orthodoxy to have a Romance language for liturgical use.

The majority of Romania's population (16,367,267, or 85.9% of those for whom data were available, according to the 2011 census data), as well as some 720,000 Moldovans, belong to the ROC.

The Montenegrin Orthodox Church (MOC; Montenegrin: Црногорска православна црква, ЦПЦ, romanized: Crnogorska pravoslavna crkva, CPC) is a canonically unrecognized Eastern Orthodox Church. Formed in 1993 and registered as a non-governmental organization, Antonije Abramović was appointed as its first metropolitan. In 2023, after some controversy, the current metropolitan, Boris Bojović, succeeded Miraš Dedeić in the role. It claims succession to an older autocephalous Montenegrin Church, which existed until the unification of the Kingdom of Serbia and Kingdom of Montenegro, later to join the Kingdom of Serbs, Croats and Slovenes in 1918.

The Montenegrin Orthodox Church has been recognized as a religious organization by the Government of Montenegro since 2001. According to a 2020 poll conducted by CEDEM, approximately 10 percent of Montenegro's Eastern Orthodox Christians have opted for membership in the Montenegrin Orthodox Church, while approximately 90 percent have opted for or stayed with the Serbian Orthodox Church, in the canonical or widely-known Eastern Orthodox Church. Notably, the creation of the MOC has been opposed by the Ecumenical Patriarchate of Constantinople. Patriarch Bartholomew I has stated that "we will never give autocephaly to the so-called 'Montenegrin Orthodox Church'" and that its then-leader Dedeić was suspended by Constantinople for adultery and embezzlement.