Descartes is one of the few geniuses in history who was able to bequeath epoch-making contributions to philosophy and to mathematics at the same time. In addition, his contributions to these areas are not independent but rather feed on each other. The mutual relation of philosophy and mathematics is reflected in the interpretation of analysis and synthesis in both mathematics and philosophy; the conception of proof; the claim that physics is nothing but geometry; the theory of eternal truths; the conception of infinity; his ontological and epistemological views on extension and number; the role of sense, imagination, and reason in mathematics and its relation to his account of human nature; the transition from a mathematical paradigm of cer...