This chapter explains the background of Marion’s work on Descartes and his interest in this philosopher. It outlines and summarizes the main arguments of all of his writings on Descartes, including the role of the important Cartesian notion of the creation of the eternal truths. Marion explains in what way Descartes’ system can be considered metaphysical and the relevance of onto-theo-logy for evaluating its metaphysical status. He also gives a brief preview of his most recent book on Descartes and provides an account of the history of the Center for Cartesian Studies in Paris. Marion shows throughout the importance of Descartes’ philosophical work and sets him in the context of other thinkers, such as Suarez, Vasquez, and Pascal.