Full communion in the context of "Branch theory"

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.

Ivan Asen II, also known as John Asen II (Bulgarian: Иван Асен II, [iˈvan ɐˈsɛn ˈftɔri]; 1190s – May/June 1241), was Emperor (Tsar) of Bulgaria from 1218 to 1241. He was still a child when his father Ivan Asen I – one of the founders of the Second Bulgarian Empire – was killed in 1196. His supporters tried to secure the throne for him after his uncle, Kaloyan, was murdered in 1207, but Kaloyan's other nephew, Boril, overcame them. Ivan Asen fled from Bulgaria and settled in the Rus' principalities.

Boril could never strengthen his rule which enabled Ivan Asen to muster an army and return to Bulgaria. He captured Tarnovo and blinded Boril in 1218. Initially, he supported the full communion of the Bulgarian Church with the Papacy and concluded alliances with the neighboring Catholic powers, Hungary and the Latin Empire of Constantinople. He tried to achieve the regency for the 11-year-old Latin Emperor, Baldwin II, after 1228, but the Latin aristocrats did not support Ivan Asen. He inflicted a crushing defeat on Theodore Komnenos Doukas of the Empire of Thessalonica, in the Battle of Klokotnitsa in 1230. Theodore's empire soon collapsed and Ivan Asen conquered large territories in Macedonia, Thessaly and Thrace.

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 Eastern Orthodox Church, officially the Orthodox Catholic Church and commonly known simply as the Orthodox Church, is a communion composed of up to seventeen separate autocephalous (self-governing) hierarchical churches that profess Eastern Orthodoxy and recognise each other as canonical (regular) 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 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 with varying degrees of autonomy (meaning they have limited self-government). Such autonomous churches maintain varying levels of dependence on their mother church, usually defined in a tomos or another 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.

The Latin Church (Latin: Ecclesia Latina) is the largest autonomous (sui iuris) particular church within the Catholic Church, whose members constitute the vast majority of the 1.3 billion Catholics. The Latin Church is one of 24 sui iuris churches in full communion with the pope; the other 23 are collectively referred to as the Eastern Catholic Churches, and they have approximately 18 million members combined.

The Latin Church is directly headed by the pope in his role as the bishop of Rome, whose cathedra as a bishop is located in the Archbasilica of Saint John Lateran in Rome, Italy. The Latin Church both developed within and strongly influenced Western culture; as such, it is sometimes called the Western Church (Latin: Ecclesia Occidentalis), which is reflected in one of the pope's traditional titles in some eras and contexts, the Patriarch of the West. It is also known as the Roman Church (Latin: Ecclesia Romana), the Latin Catholic Church, and in some contexts as the Roman Catholic Church (though this name can also refer to the Catholic Church as a whole).

The Holy See (Latin: Sancta Sedes, lit. 'Holy Chair', Ecclesiastical Latin pronunciation: [ˈsaŋkta ˈsedes]; Italian: Santa Sede [ˈsanta ˈsɛːde]), also called the See of Rome, the Petrine See or the Apostolic See, is the central governing body of the Catholic Church and Vatican City. It encompasses the office of the pope as the bishop of the apostolic episcopal see of Rome, and serves as the spiritual and administrative authority of the worldwide Catholic Church and Vatican City. Under international law, the Holy See holds the status of a sovereign juridical entity.

According to Catholic tradition and historical records, the Holy See was founded in the first century by Saint Peter and Saint Paul. By virtue of the doctrines of Petrine and papal primacy, it is the focal point of full communion for Catholics around the world. The Holy See is headquartered in, operates from, and exercises "exclusive dominion" over Vatican City, an independent city-state enclaved in Rome, and of which the pope is the head of state.

The Catholic Church is "the Catholic Communion of Churches, both Roman and Eastern, or Oriental, that are in full communion with the Bishop of Rome (the pope)." This communion comprises the Latin Church (the Roman or Western Church) as well as 23 Eastern Catholic Churches, canonically called sui juris churches, each led by either a patriarch or a major archbishop in full communion with the pope. Historically, these bodies separated from Eastern Christian communions, either to remain in or to return to full communion with the Catholic Church. The Vatican II decree on Eastern Catholic Churches, however, explicitly recognizes them as churches and not just rites within the Catholic Church. This communion "exists among and between the individual Churches and dioceses of the universal Catholic Church. Its structural expression is the College of Bishops, each of whom represents and embodies his own local church." In addition to Eastern Catholic Churches, the Catholic Church oversees the Catholic Charismatic Renewal, the largest Charismatic movement of a single institution in 2020, with over 100 million members, primarily in the Global South. The Catholic Church is also described as an "amalgam of parts" (i.e., thousands of individual dioceses and religious orders) globally dispersed, but in communion with Rome.

The Catholic Church is the "world's oldest continuously functioning international institution." It is also the largest non-government provider of education and health care in the world, while the diplomatic status of the Holy See facilitates access to its vast international network of charities. These entities include 5,000 hospitals, 10,000 orphanages, 95,000 elementary schools and 47,000 secondary schools.

The Eastern Catholic Churches or Oriental Catholic Churches, also known as the Eastern-Rite Catholic Churches, Eastern Rite Catholicism, or simply the Eastern Churches, are 23 Eastern Christian autonomous (sui iuris) particular churches of the Catholic Church in full communion with the pope in Rome. Although they are distinct theologically, liturgically, and historically from the Latin Church, they are all in full communion with it and with each other. Eastern Catholics are a minority within the Catholic Church; of the 1.3 billion Catholics in communion with the pope, approximately 18 million are members of the Eastern churches. The largest numbers of Eastern Catholics are found in Eastern Europe, Eastern Africa, the Middle East, and India. As of 2022, the Syro-Malabar Church is the largest Eastern Catholic Church, followed by the Ukrainian Greek Catholic Church.

With the exception of the Maronite Church, the Eastern Catholic Churches are groups that, at different points in the past, used to belong to the Eastern Orthodox Church, the Oriental Orthodox churches, or the Church of the East; these churches underwent various schisms through history. Eastern Catholic Churches that were formerly part of other communions have been points of controversy in ecumenical relations with the Eastern Orthodox and other non-Catholic churches. The five historic liturgical traditions of Eastern Christianity, namely the Alexandrian Rite, the Armenian Rite, the Byzantine Rite, the East Syriac Rite, and the West Syriac Rite, are all represented within Eastern Catholic liturgy. On occasion, this leads to a conflation of the liturgical word "rite" and the institutional word "church". Some Eastern Catholic jurisdictions admit members of churches not in communion with Rome to the Eucharist and the other sacraments.