Hypostatic union (from the Greek: ὑπόστασις hypóstasis, "person, subsistence") is a technical term in Christian theology employed in mainstream Christology to describe the union of Christ's humanity and divinity in one hypostasis, or individual personhood.

The most basic explanation for the hypostatic union is Jesus Christ being both fully God and fully man. He is both perfectly divine and perfectly human and has two complete and distinct natures at once.

The Athanasian Creed recognized this doctrine and affirmed its importance by stating, "He is God from the essence of the Father, begotten before time; and he is human from the essence of his mother, born in time; completely God, completely human, with a rational soul and human flesh; equal to the Father as regards divinity, less than the Father as regards humanity. Although he is God and human, yet Christ is not two, but one. He is one, however, not by his divinity being turned into flesh, but by God's taking humanity to himself. He is one, certainly not by the blending of his essence, but by the unity of his person. For just as one human is both rational soul and flesh, so too the one Christ is both God and human."