The Ethiopian Orthodox Tewahedo Church (የኢትዮጵያ ኦርቶዶክስ ተዋሕዶ ቤተ ክርስቲያን, Yäityop'ya ortodoks täwahedo bétäkrestyan) is the largest of the Oriental Orthodox Churches. One of the few Christian churches in sub-Saharan Africa originating before European colonization of the continent, the Ethiopian Orthodox Tewahedo Church dates back to the acceptance of Christianity by the Kingdom of Aksum in 330, and has between 36 million and 49.8 million adherents in Ethiopia. It is a founding member of the World Council of Churches. The Ethiopian Orthodox Tewahedo Church is in communion with the other Oriental Orthodox churches (the Eritrean Orthodox Tewahedo Church, the Coptic Orthodox Church of Alexandria, the Malankara Orthodox Syrian Church, the Armenian Apostolic Church, and the Syriac Orthodox Church).
The Ethiopian Orthodox Tewahedo Church had been administratively part of the Coptic Orthodox Church of Alexandria from the first half of the 4th century until 1959, when it was granted autocephaly with its own patriarch by Pope Cyril VI of Alexandria, Pope of the Coptic Orthodox Church.
Tewahedo (Geʽez: ተዋሕዶ) is a Geʽez word meaning "united as one". This word refers to the Oriental Orthodox belief in the one perfectly unified nature of Christ; i.e., a complete union of the divine and human natures into one nature is self-evident in order to accomplish the divine salvation of mankind, as opposed to the "two natures of Christ" belief commonly held by the Latin and Eastern Catholic, Eastern Orthodox, Anglican, Lutheran, and most other Protestant churches. The Oriental Orthodox Churches adhere to a miaphysitic Christological view followed by Cyril of Alexandria, the leading protagonist in the Christological debates of the 4th and 5th centuries, who advocated mia physis tou theou logou sesarkōmenē, or "one (mia) nature of the Word of God incarnate" (μία φύσις τοῦ θεοῦ λόγου σεσαρκωμένη) and a hypostatic union (ἕνωσις καθ' ὑπόστασιν, henōsis kath hypostasin).