Spinoza’s Principles of Cartesian Philosophy is often presented simply as an interpretation of Descartes’ Principia that does not reveal anything significant about Spinoza’s philosophy and its development. This paper, however, shows that Spinoza altered Descartes’ text in a way congruent with what he would later write in his Theological Political Treatise and the Ethics. More precisely, this paper concentrates not on what Spinoza added to Descartes’ texts but on how he presented them. The paper furthermore examines questions that were obviously important for Descartes but absent in Spinoza’s interpretation. Finally, this paper examines two concrete examples to show that Spinoza’s adaptations function as an unmasking of Descartes’ physics.