The Council of Chalcedon, a Christian ecumenical council, opened, and went on to repudiate the Eutychian doctrine of monophysitism and set forth the Chalcedonian Creed.

The Council of Chalcedon was the fourth ecumenical council of the Christian Church. It was convoked by the Roman emperor Marcian. The council convened in the city of Chalcedon, Bithynia from 8 October to 1 November 451. The council was attended by over 520 bishops or their representatives, making it the largest and best-documented of the first seven ecumenical councils. The principal purpose of the council was to re-assert the teachings of the ecumenical Council of Ephesus against the teachings of Eutyches and Nestorius. Such doctrines viewed Christ's divine and human natures as separate (Nestorianism) or viewed Christ as solely divine (monophysitism).

An ecumenical council, also called general council, is a meeting of bishops and other church authorities to consider and rule on questions of Christian doctrine, administration, discipline, and other matters in which those entitled to vote are convoked from the whole world (oikoumene) and which secures the approbation of the whole Church.

Eutyches or Eutyches of Constantinople was a presbyter and archimandrite at Constantinople. He first came to notice in 431 at the First Council of Ephesus, for his vehement opposition to the teachings of Nestorius. Eutyches was condemned for having adopted a polar opposite view of Nestorianism, where the two natures of Christ fuse together to form one, single Divine nature, dubbed Monophysitism. This was condemned at the Council of Chalcedon and Third Council of Ephesus. He himself, however, would reject this interpretation of his thought.

Monophysitism or monophysism is a Christological doctrine that states that there was only one nature—the divine—in the person of Jesus Christ, who was the incarnated Word. It is rejected as heretical by the Catholic Church, Eastern Orthodox Church, Anglicanism, Lutheranism, Reformed Christianity (Calvinist), and all mainstream Protestant denominations, which hold to the dyophysitism of the 451 Council of Chalcedon—as well by Oriental Orthodoxy, which holds to miaphysitism.