John Zizioulas is not only a prolific writer but arguably one of the most original and influential Orthodox scholars of our present time. His originality can be most clearly observed in his development of a personal and relational ontology. Central to this approach is his assertion that the Father as cause should be understood as the one God rather than the divine ousia. Zizioulas subsequently asserts that the divine ousia should be understood in terms of divine communion. While this approach might be original, it is not without its difficulties, not least the possible implication that there are two different Gods. It is our contention that this problem arises out of a failure by Zizioulas to adequately distinguish between two distinct types of divine unity particularly located in the writings of the Cappadocian Fathers. The first is located solely in the ousia and ensures the ontological oneness of God, the second may be observed in the relational role of the Father as a point of reference for the Son and the Spirit. Finally, although these two forms of unity are identified by the Cappadocians we will suggest that the second is more adequately located with the Spirit by Augustine.