In Chapter 7, I consider Arnauld’s modal metaphysics and his actualist view of possibility. Specifically, I argue that Arnauld endorses an essence-based modal actualism. Arnauld develops his view in correspondence with Gottfried Leibniz, so I begin the chapter with a discussion of the beginning of the correspondence, Leibniz’s account of the complete concept theory of substance as well as his account of modality. I then consider Arnauld’s response to Leibniz in three parts: his account of his own nature, his rejection of purely possible substances, and his positive account. I conclude by suggesting Arnauld’s modal metaphysics, with a few modifications, has much to be said for it and could be developed into a plausible view in its own right.