Russian Orthodox Church in the context of "Doukhobors"

Eastern Orthodoxy, otherwise known as Eastern Orthodox Christianity or Byzantine Christianity, is one of the three main branches of Chalcedonian Christianity, alongside Catholicism and Protestantism. Like the Pentarchy of the first millennium, the mainstream (or "canonical") Eastern Orthodox Church is organised into autocephalous churches independent from each other. In the 21st century, the number of mainstream autocephalous churches is seventeen; there also exist autocephalous churches unrecognized by those mainstream ones. Autocephalous churches choose their own primate. Autocephalous churches can have jurisdiction (authority) over other churches, some of which have the status of "autonomous" which means they have more autonomy than simple eparchies.

Many of these jurisdictions correspond to the territories of one or more modern states; the Patriarchate of Moscow, for example, corresponds to Russia and some of the other post-Soviet states. They can also include metropolises, bishoprics, parishes, monasteries, or outlying metochia corresponding to diasporas that can also be located outside the country where the primate resides (e.g., the case of the Ecumenical Patriarchate of Constantinople whose canonical territory is located partly in northern Greece and the east); sometimes they overlap (the case of Moldova where the jurisdictions of the patriarchs of Bucharest and of Moscow overlap).

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.

Moldova's constitution provides for freedom of religion and complete separation of church and state, though the constitution cites the "exceptional importance" of Eastern Orthodox Christianity. Discrimination on the basis of religious affiliation is illegal, and incitement to religious and ethnic hatred was made illegal in May 2022. Moldovans are overwhelmingly adherents of Eastern Orthodoxy. According to the 2024 Moldovan census, 95.2 per cent of the country reported to be of the Eastern Orthodox Christian faith. Of this number, around eighty to 90 per cent of Orthodox Moldovans belong to the Moldovan Orthodox Church (formally known as Metropolis of Chișinău and All Moldova) which is subordinate to the Russian Orthodox Church, and has played a powerful role in deepening Russia's influence in Moldova. The remaining 10–20 per cent of Orthodox Moldovans belong to the Metropolis of Bessarabia, which is subordinate to the Romanian Orthodox Church.

Christianity in Russia is the most widely professed religion in the country. The largest tradition is the Russian Orthodox Church. According to official sources, there are 170 eparchies of the Russian Orthodox Church, 145 of which are grouped in metropolitanates. There are from 500,000 to one million Old Believers, who represent an older form of Russian Orthodox Christianity, and who separated from the Orthodox Church in the 17th century as a protest against Patriarch Nikon's church reforms.

The Catholic Church estimates that there are from 600,000 to 1.5 million Catholics in the country, exceeding government estimates of about 140,000. There is one Catholic Archdiocese, Mother of God at Moscow, with three suffragan dioceses (Saint Clement at Saratov, Saint Joseph at Irkutsk, Transfiguration at Novosibirsk) and the Apostolic Prefecture of Yuzhno-Sakhalinsk. According to the Slavic Center for Law and Justice, Protestants make up the second or third largest group of Christians in Russia, with approximately 3,500 organizations and more than 1 million followers. A large number of missionaries operating in the country are from Protestant denominations.

Church Slavonic is the conservative Slavic liturgical language used by the Eastern Orthodox Church in Belarus, Bulgaria, North Macedonia, Montenegro, Poland, Russia, Ukraine, Serbia, the Czech Republic and Slovakia, Slovenia and Croatia. The language appears also in the services of the Russian Orthodox Church Outside of Russia, the American Carpatho-Russian Orthodox Diocese, and occasionally in the services of the Orthodox Church in America.

In addition, Church Slavonic is used by some churches which consider themselves Orthodox but are not in communion with the Orthodox Church, such as the Montenegrin Orthodox Church and the Russian True Orthodox Church. The Russian Old Believers and the Co-Believers also use Church Slavonic.

The Patriarch of Moscow and all Rus' (Russian: Патриарх Московский и всея Руси, romanized: Patriarkh Moskovskiy i vseya Rusi), also known as the Patriarch of Moscow and all Russia, is the title of the primate of the Russian Orthodox Church (ROC). It is often preceded by the honorific "His Holiness". As the ordinary of the diocese of Moscow, the office holder's direct canonical remit extends only to Moscow; however, as the patriarch, the office holder has a number of church-wide administrative powers as laid down by the charter of the ROC.

The patriarchate was established in 1589 when the status of the Russian metropolitan was elevated, with Job becoming the first patriarch. The patriarchate was abolished in 1721 by Peter the Great and replaced with the Most Holy Synod as the supreme governing body of the ROC, before being restored on 10 November [O.S. 28 October] 1917, by decision of the All-Russian Local Council. The current patriarch is Kirill, who acceded to the position in 2009.