This chapter explores some key issues within Descartes’s theory of cognition. The starting-point is a recent interpretation, according to which Descartes is part of a tradition of theorizing about human cognition, beginning from the idea that we are in principle capable of articulating or grasping the basic order of reality. Earlier readings often take Descartes to question whether we have any cognitive access to reality at all. On the new reading, Descartes instead defends a robust conception of our cognitive relation to reality—our cognition needs to be “determined by reality,” as John Carriero puts it. One important element of Carriero’s interpretation is that Descartes’s notion of idea is to be understood along the lines of the Aristotelian doctrine of formal identity between cognizer and cognized. Here it is argued that retaining the latter doctrine faces some difficulties, given the novel conception of the structure of reality defended by Descartes. This chapter proposes that he needs an alternative account of what it is for a cognizer to be determined by reality. Attending to some important differences between the innate idea of extension and that of God, the chapter concludes that Descartes may not have a fully worked-out account of his own. Considering some of the problems inherent in his views can, however, shed light on the, from our contemporary perspective, peculiar role both Spinoza and Leibniz give to God in accounting for cognition.