Chalcedonian Christianity is the religious doctrine of those Christian churches which accept the Definition of Chalcedon (from the year 451 AD). This teaching is concerned with the relation of the divine nature to the human nature in the person of Jesus Christ. While most modern Christian churches are Chalcedonian, in the 5th – 8th centuries the ascendancy of Chalcedonian Christology was not always certain.

The dogmatical disputes raised during the Council of Chalcedon led to the Chalcedonian Schism, and as a matter of course to the formation of the non-Chalcedonian body of churches known as Oriental Orthodoxy. The Chalcedonian churches were the ones that remained united with Rome, Constantinople and the three Orthodox patriarchates of the East (Alexandria, Antioch and Jerusalem). Together, these five patriarchates became the organizational foundation of Chalcedonian Christianity, and during the reign of the Emperor Justinian I they were recognized as the Pentarchy, the official leadership of the Christian Church.

Today, the great majority of Christian churches and organizations are descended from the Pentarchy, and subscribe to Chalcedonian Christianity. Examples include the Catholic Church, the Eastern Orthodox Church, and most Protestant denominations.

The groups that rejected the Chalcedonian definition were the majority of the Armenian, Coptic, and Ethiopian Christians, together with a part of the Syriac Christians. Today, these groups are known collectively as the Oriental Orthodox churches. Some Armenian Christians (especially in the region of Cappadocia and Trebizond inside the Byzantine Empire) did accept the decisions of the Council of Chalcedon and engaged in polemics against the Armenian Apostolic Church.

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