René Descartes is best remembered today for writing 'I think, therefore I am', but his main contribution to the history of ideas was his effort to construct a philosophy that would be sympathetic to the new sciences that emerged in the seventeenth century. To a great extent he was the midwife to the Scientific Revolution and a significant contributor to its key concepts. In four major publications, he fashioned a philosophical system that accommodated the needs of these new sciences and thereby earned the unrelenting hostility of both Catholic and Calvinist theologians, who relied on the scholastic philosophy that Descartes hoped to replace. His contemporaries claimed that his proofs of God's existence in the Meditations were so unsuccessful that he must have been a cryptic atheist and that his discussion of skepticism served merely to fan the flames of libertinism. This is the first biography in English that addresses the full range of Descartes' interest in theology, philosophy and the sciences and that traces his intellectual development through his entire career.