Rene Descartes (1596-1650) was a highly influential philosopher, mathematician, and scientist and is regarded as the "Father of modern philosophy and mathematics". His invention of analytical geometry - the basis of calculus - made physics, as we know it today, possible; he perfected the method of proposing and testing hypotheses, which has become the basis of all modern science. He is perhaps most famous for his philosophical thinking - and his conclusion "I think, therefore I am." "Cogito, Ergo Sum" is the first biography of Descartes to be published since 1920 that uses extensive original field and archival research. It is explicitly the life of Descartes, in the flesh and blood, rather than a technical analysis of his philosophical, scientific, and mathematical ideas - and a compelling read.