Descartes is best remembered for 'I think, therefore I am', but his main contribution to the history of ideas was to construct a philosophy that would be sympathetic to the emergence of the new sciences in the seventeenth century. He was midwife to the Scientific Revolution and a significant contributor to its key concepts, fashioning a philosophy that accommodated these needs whilst earning the unrelenting hostility of Catholic and Calvinist theologians. His contemporaries claimed that his proof of God's existence was so unsuccessful that he must have been a cryptic atheist, and that his skepticism served merely to fan the flames of libertinism. Descartes died in obscurity but became one of the most famous of philosophers, a status that he enjoys today. This is the first biography in English to address the full range of Descartes' interest in theology, philosophy, and the sciences, tracing his intellectual development throughout his career.