Descartes' Discourse on Methodhas long been regarded as a seminal contribution to modern philosophy. We can now see that it is also one of the key texts in the 'scientific revolution' of the seventeenth century. Rene Descartes (1596-1650) did major research in optics, geometry, astronomy and physiology, although he published nothing until he was over forty. The Discourseforms the preface to his first collection of scientific papers (1637), sketching in a new method based on hypothesis and deduction which was soon to replace traditional techniques derived from Aristotle. This edition puts the work in context, by including extracts from Descartes' correspondence, the Rules for Guiding One's Intelligenceand from The World- a posthumously published summary of his physical theories. The age of Newton marks one of the great turning points in intellectual history; Descartes has a key place at its very heart. Also by Descartes is the companion volume, Meditations and other Metaphysical Writings.