A number of thinkers in recent decades have argued that, in light of the Trinity, we can see that God's being is communion. Particularly effective was John D. Zizioulas, whose Trinitarian ontology centered on communion. Some skeptical of this claim have invoked Aquinas as a source for countering an ontology of communion. I argue that, while Thomas never explicitly affirms that the divine being is communion, he can give us deep resources for reaching this conclusion. Indeed, he can ultimately lead us towards a divine being which is more thoroughly a matter of communion—and towards an ontology which is more radically Trinitarian—than anything we find in Zizioulas.