 René Descartes (1596–1650) is widely regarded as the father of modern philosophy. His noteworthy contributions extend to mathematics and physics. This entry focuses on his philosophical contributions in the theory of knowledge. Specifically, the focus is on the epistemological project of his famous work, Meditations on First Philosophy. Descartes circulated the Meditations to other philosophers for objections and comments. He responded with detailed replies that provide a rich source of further information about the original work. Indeed, six sets of objections and replies were published with the first edition of the Meditations (1641), and a seventh set was added with the second edition (1642).