Nestorian Christians

Church of the East
Syriac: ܥܕܬܐ ܕܡܕܢܚܐ‎
Ruins of the ancient city and see Assur.
Classification	Eastern Christian
Orientation	Syriac Christian
Head	Patriarchs the East
Region	Middle East, South India, Far East
Liturgy	East Syrian Rite
Headquarters	Assur (Ottoman Empire)
Founder	Archbishop Nestorius
Origin	Nestorian Schism (431–544) Sasanian Empire
Merger of	Catholic Church (1552), as the Church of Assyria and Mosul
Other name(s)	Nestorian Church

The Church of the East (Syriac: ܥܕܬܐ ܕܡܕܢܚܐ‎ Ēdtāʾ d-Maḏenḥā), also known as the Nestorian Church, is a Christian church within the Syriac tradition of Eastern Christianity. It was the Christian church of the Sassanian Empire, and quickly spread widely through Asia. Between the 9th and 14th centuries, the Church represented the world's largest Christian church in terms of geographical extent, with dioceses stretching from the Mediterranean Sea to China and India. Several modern churches claim continuity with the historical Church of the East.

The background of the establishment of the Church of the East is considered to the first and third centuries among the early Assyrian Christian communities in the Parthian Empire's province of Mesopotamia and the Sasanian province of Asōristān (Assyria) and the small independent Neo-Assyrian kingdoms of Osroene, Adiabene, Beth Garmai, Beth Nuhadra and Assur.

The Church of the East was headed by the Patriarch of the East, continuing a line that, according to tradition, stretched back to the Apostolic Age. Liturgically, the church adhered to the East Syrian Rite, and theologically, it adopted the doctrine of Nestorianism, which emphasises the separateness of the divine and human natures of Jesus. This doctrine and its namesake, Nestorius (386–451), were condemned by the Council of Ephesus in 431, leading to the Nestorian Schism and a subsequent exodus of Nestorius' supporters to Sasanian Persia. The existing Christians in Persia welcomed these refugees and gradually adopted Nestorian doctrine by the 5th century, leading the Church of Persia to be known alternately as the Nestorian Church.