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 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.
Therefore, following the holy fathers, we all with one accord teach men to acknowledge one and the same Son, our Lord Jesus Christ, at once complete in Godhead and complete in manhood, truly God and truly man, consisting also of a reasonable soul and body; of one substance with the Father as regards his Godhead, and at the same time of one substance with us as regards his manhood; like us in all respects, apart from sin; as regards his Godhead, begotten of the Father before the ages, but yet as regards his manhood begotten, for us men and for our salvation, of Mary the Virgin, the God-bearer; one and the same Christ, Son, Lord, Only-begotten, recognized in two natures, without confusion, without change, without division, without separation; the distinction of natures being in no way annulled by the union, but rather the characteristics of each nature being preserved and coming together to form one person and subsistence, not as parted or separated into two persons, but one and the same Son and Only-begotten God the Word, Lord Jesus Christ; even as the prophets from earliest times spoke of him, and our Lord Jesus Christ himself taught us, and the creed of the fathers has handed down to us.