Nestorianism is a Christological doctrine advanced by Nestorius, Patriarch of Constantinople from 428??31. The doctrine, which was informed by Nestorius's studies under Theodore of Mopsuestia at the School of Antioch, emphasizes the disunion between the human and divine natures of Jesus. Nestorius' teachings brought him into conflict with some other prominent church leaders, most notably Cyril of Alexandria, who criticized especially his rejection of the title Theotokos ('Mother of God') for the Virgin Mary.

Nestorius and his teachings were eventually condemned as heretical at the First Council of Ephesus in 431 and the Council of Chalcedon in 451, leading to the Nestorian Schism in which churches supporting Nestorius broke with the rest of the Christian Church. Afterward many of Nestorius' supporters relocated to Sassanid Persia, where they affiliated with the local Christian community, known as the Church of the East. Over the next decades the Church of the East became increasingly Nestorian in doctrine, leading it to be known alternately as the Nestorian Church.

Christianity came to South India long before European colonialism. Malabar still has a Christian community dating back to the Apostle Thomas. Marco Polo saw a tomb with a Nestorian cross which was shown to him as the tomb of St.Thomas in South India.