The Chalcedonian Creed was adopted at the Council of Chalcedon in 451 in Asia Minor as a response to certain heretical views concerning the nature of Christ. This Council of Chalcedon is the fourth of the seven ecumenical councils accepted by Eastern Orthodox, Catholic, and many Protestant Christian churches. It is the first Council not recognized by any of the Oriental Orthodox churches.
The Chalcedonian Creed was written amid controversy between the western and eastern churches over the meaning of the incarnation (see Christology), the ecclesiastical influence of the Byzantine emperor, and the supremacy of the Roman Pope. The western churches readily accepted the creed, but some eastern churches did not. The adopted Creed specifically maintained the two distinct natures of Christ (divine and human) over against teaching of Eutyches -- that Christ had only one nature, a mixture of human and divine. Eutychianism is also known as monophysitism from monos (single) and physis (nature), which confuses both Christs true humanity and his true deity.
An English translation of the Creed
We, then, following the holy Fathers, all with one consent, teach men to confess one and the same Son, our Lord Jesus Christ, the same perfect in Godhead and also perfect in manhood; truly God and truly man, of a reasonable soul and body; consubstantial with us according to the manhood; in all things like unto us, without sin; begotten before all ages of the Father according to the Godhead, and in these latter days, for us and for our salvation, born of the virgin Mary, the mother of God, according to the manhood; one and the same Christ, Son, Lord, Only-begotten, to be acknowledged in two natures, inconfusedly, unchangeably, indivisibly, inseparably; the distinction of natures being by no means taken away by the union, but rather the property of each nature being preserved, and concurring in one Person and one Subsistence, not parted or divided into two persons, but one and the same Son, and only begotten, God the Word, the Lord Jesus Christ, as the prophets from the beginning have declared concerning him, and the Lord Jesus Christ himself taught us, and the Creed of the holy Fathers has handed down to us.