According to St. John Damascene, the union in Christ is “a true union of [the two natures] in one composite hypostasis of the Son of God.” It is our purpose to examine what he means by this phrase, “composite hypostasis,” (σύνθετος ὑπόστασις) and how he applies it to Christ. We’ll approach this matter by examining the meaning of “composite” in his works, the meaning of “hypostasis”, the two kinds of unions he describes, and how this fits in his Christology. We argue that St. John uses “composite hypostasis” to mean a complete whole which is composed of parts that retain their full integrity, each part bearing its own nature, and its own natural properties and energies. While the parts are distinct, they are not divided, and thus the whole is internally united. St. John views this as the traditional patristic understanding of Christ: since Christ’s two natures have incompatible properties, each nature retained its own integrity within the union.