The Russian Orthodox Church (ROC; Russian: Ру́сская правосла́вная це́рковь, tr. Rússkaya pravoslávnaya tsérkov), alternatively legally known as the Moscow Patriarchate (Russian: Моско́вский патриарха́т, tr. Moskóvskiy patriarkhát), is one of the autocephalous Eastern Orthodox churches, in full communion with other Eastern Orthodox patriarchates. The Primate of the ROC is the Patriarch of Moscow and all Rus'. The ROC, as well as the primate thereof, officially ranks fifth in the Orthodox order of precedence, immediately below the four ancient Patriarchates of the Greek Orthodox Church, those of Constantinople, Alexandria, Antioch, and Jerusalem. The official Christianization of Kievan Rus' widely seen as the birth of the ROC is believed to have occurred in 988 through the baptism of the Kievan prince Vladimir and his people by the clergy of the Ecumenical Patriarchate whose constituent part the ROC remained for the next six centuries, while the Kievan see remained in the jurisdiction of the Ecumenical Patriarchate until 1686.
The ROC currently claims its exclusive jurisdiction over the Orthodox Christians, irrespective of their ethnic background, who reside in the former member republics of the Soviet Union, excluding Georgia and Armenia, although this claim is disputed in such countries as Estonia, Moldova and Ukraine and consequently parallel canonical Orthodox jurisdictions exist in those: Estonian Apostolic Orthodox Church and Metropolis of Bessarabia, respectively. It also exercises ecclesiastical jurisdiction over the autonomous Church of Japan and the Orthodox Christians resident in the People's Republic of China. The ROC branches in Belarus, Estonia, Latvia, Moldova and Ukraine since the 1990s enjoy various degrees of self-government, albeit short of the status of formal ecclesiastical autonomy. In Ukraine, ROC (represented by the Ukrainian Orthodox Church) has tensions with schismatic groups supported by the current government, while it enjoys the position of numerically dominant religious organisation.
The ROC should not be confused with the Orthodox Church in America (OCA), another autocephalous Orthodox Church (since 1970, albeit not universally recognised in this status), that traces its existence in North America to the time of the Russian missionaries in Alaska (then part of the Russian Empire) in the late 18th century, and still adheres to the ROC liturgical tradition.
The ROC should also not be confused with the Russian Orthodox Church Outside Russia (also known as the Russian Orthodox Church Abroad, or ROCOR), headquartered in New York, New York, U.S.A. The ROCOR was instituted in the 1920s by Russian communities outside then Communist Russia, which refused to recognize the authority of the Moscow Patriarchate then de facto headed by Metropolitan Sergius Stragorodsky. The two Churches reconciled on May 17, 2007; the ROCOR is now a self-governing part of the Russian Orthodox Church.
The Christian community that developed into what is now known as the Russian Orthodox Church is traditionally said to have been founded by the Apostle Andrew, who is thought to have visited Scythia and Greek colonies along the northern coast of the Black Sea. According to one of the legends, Andrew reached the future location of Kiev and foretold the foundation of a great Christian city. The spot where he reportedly erected a cross is now marked by St. Andrew's Cathedral.
By the end of the first millennium AD, eastern Slavic lands started to come under the cultural influence of the Eastern Roman Empire. In 863–69, the Byzantine Greek monks Saint Cyril and Saint Methodius, both from Greek Macedonia, translated parts of the Bible into Old Church Slavonic language for the first time, paving the way for the Christianization of the Slavs and Slavicized peoples of Eastern Europe, the Balkans, Ukraine, and Southern Russia. There is evidence that the first Christian bishop was sent to Novgorod from Constantinople either by Patriarch Photius or Patriarch Ignatios, c. 866–67.
By the mid-10th century, there was already a Christian community among Kievan nobility, under the leadership of Byzantine Greek priests, although paganism remained the dominant religion. Princess Olga of Kiev was the first ruler of Kievan Rus′ to convert to Christianity, either in 945 or 957. Her grandson, Vladimir of Kiev, made Rus' officially a Christian state. The official Christianization of Kievan Rus' is widely believed to have occurred in 988 AD, when Prince Vladimir was baptised himself and ordered his people to be baptised by the priests from the Eastern Roman Empire.