Eastern Christian in the context of "Liturgy of Saint James"

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.

The Syriac language (/ˈsɪriæk/ SIRR-ee-ak; Classical Syriac: ܠܫܢܐ ܣܘܪܝܝܐ, romanized: Leššānā Suryāyā), also known natively in its spoken form in early Syriac literature as Edessan (Urhāyā), the Mesopotamian language (Nahrāyā) and Aramaic (Aramāyā), is an Eastern Middle Aramaic dialect. Classical Syriac is the academic term used to refer to the dialect's literary usage and standardization, distinguishing it from other Aramaic dialects also known as 'Syriac' or 'Syrian'. In its West-Syriac tradition, Classical Syriac is often known as leššōnō kṯoḇonōyō (lit. 'the written language or the book language') or simply kṯoḇonōyō, or kṯowonōyō, while in its East-Syriac tradition, it is known as leššānā ʔatīqā (lit. 'the old language') or saprāyā (lit. 'scribal or literary').

It emerged during the first century AD from a local Eastern Aramaic dialect that was spoken in the ancient region of Osroene, centered in the city of Edessa. During the Early Christian period, it became the main literary language of various Aramaic-speaking Christian communities in the historical region of Ancient Syria and throughout the Near East. As a liturgical language of Syriac Christianity, it gained a prominent role among Eastern Christian communities that used both Eastern Syriac and Western Syriac rites. Following the spread of Syriac Christianity, it also became a liturgical language of eastern Christian communities as far as India and China. It flourished from the 4th to the 8th century, and continued to have an important role during the next centuries, but by the end of the Middle Ages it was gradually reduced to liturgical use, since the role of vernacular language among its native speakers was overtaken by several emerging Neo-Aramaic languages.

Melkite (/ˈmɛlkaɪt/) or Melchite churches are various Eastern Christian churches of the Byzantine Rite, and their members. The name comes from the Central Semitic root m-l-k 'royal', referring to the loyalty to the Byzantine emperor, and became a denominational designation for Christians who accepted imperial religious policies, notably the Council of Chalcedon (451).

Originally, during the Early Middle Ages, Melkites used both Koine Greek and Aramaic (Classical Syriac & Syro-Palestinian) language in their religious life, and initially employed the Antiochian rite in their liturgy, but later (10th–11th century) accepted the Constantinopolitan rite, and incorporated Arabic in parts of their liturgical practices.

The Ancient Church of the East (ACE) is an Eastern Christian denomination. It branched from the Assyrian Church of the East in 1964, under the leadership of Mar Toma Darmo (d. 1969). It is one of three Assyrian Churches claiming continuity with the historical Church of the East, in addition to the Assyrian Church of the East and the Chaldean Catholic Church. Since 1969, the see of the Ancient Church of the East is headquartered in Baghdad.

The Cossacks are a predominantly East Slavic, Eastern Christian people, originating from the Pontic–Caspian steppe of eastern Ukraine and southern Russia. Cossacks played an important role in defending the southern borders of Ukraine and Russia, countering the Crimean-Nogai raids, alongside economically developing steppe regions north of the Black Sea and around the Azov Sea. Historically, they were a semi-nomadic and semi-militarized people, who were allowed a great degree of self-governance in exchange for military service under the nominal suzerainty of various Eastern European states. Although numerous ethnic, linguistic and religious groups came together to form the Cossacks, most of them gradually coalesced and Slavicized, thereby adopting East Slavic culture, East Slavic languages and Eastern Orthodox Christianity.

The rulers of the Polish–Lithuanian Commonwealth and Russian Empire endowed Cossacks with certain special privileges in return for the military duty to serve in the irregular troops: Zaporozhian Cossacks were mostly infantry soldiers, using war wagons, while Don Cossacks were mostly cavalry soldiers. The various Cossack groups were organized along military lines, with large autonomous groups called hosts. Each host had a territory consisting of affiliated villages called stanitsas.