Descartes’s causal theory is often taken to announce modernity by radically breaking with the Aristotelian past. Specifically, Descartes is often taken to reject the full Aristotelian causal theory in favor of the efficient causes characteristic of mechanistic physics and the activity of minds. In this chapter, I argue against this view by showing that Descartes endorses an avowedly Aristotelian notion of formal causation. First, I articulate Cartesian formal causation in light of its Aristotelian background, and I show that Descartes endorses (...) what Francisco Suárez termed metaphysical formal causal explanation. Then, I argue against taking formal causation to be a peripheral explanatory notion for Descartes by showing it to be both well-attested textually and part and parcel of his Platonic intellectualism. I conclude by suggesting some further contexts in which this Cartesian notion of formal causation could be profitably wielded. (shrink)