Ren Descartes is famous as the philosopher who was prepared to doubt everything - even his own physical existence. Most people also know that he said, I think, therefore I am, even if they are not always sure why he said this, or what he really meant by it. Introducing Descartes explains what Descartes doubted, and why he is usually called the father of modern philosophy. It is a clear and accessible guide to all the puzzling questions that Descartes asked about human beings and their place in the world. It gives a lucid account of Descartes' contributions to modern science, mathematics and the Philosophy of Mind, and is essential reading for anybody who wants to understand how contemporary philosophy began. It also reveals why Descartes liked to do all of his serious thinking in bed.