It is commonly argued by Christian philosophers and theologians that the traditional doctrine of divine simplicity is incompatible with the orthodox doctrine of the Trinity. First, it would seem that the presence of relations in God suggests a composition of substance and accidents in him. Second, if all that is in God is God, as simplicity claims, then it would seem that one could not maintain the real distinctions between the divine persons, as the Trinity requires. In answer to these challenges this article seeks to recover Thomas Aquinas' and the Reformed scholastics' emphasis upon the subsistence and pure actuality of the personal relations in God. The article concludes that while God's personal relations are really distinct from each other, there is no real distinction between the personal relations and the divine substance and that the Trinity and the doctrine of divine simplicity are thus agreeable.