René Descartes: The Complete Correspondence in English Translation is the first complete English translation of the extant correspondence of the polymath René Descartes, who excelled in all areas of philosophy, the sciences, and mathematics. The translation is based on the best available editions, modified by several other sources. It is accompanied by an editorial apparatus consisting of cross-references and brief biographies of the correspondents. Descartes' correspondence elaborates his views, providing a crucial resource for students, teachers, and scholars in philosophy, history of philosophy, and history of science and mathematics. Volume I presents correspondence from the period 1619 to 1638. The letters begin with exchanges between Descartes and the physico-mathematician Isaac Beeckman, the essayist Guez de Balzac, the lens maker Jean Ferrier, and Descartes' future primary correspondent Marin Mersenne. It includes letters to high ranking Oratorians. One can also see the beginnings of Descartes' relations with Constantijn Huygens, who will be Descartes' other chief correspondent. One can also trace the developments of Descartes' early unpublished works on metaphysics, physics, and human biology, together with his reaction to the condemnation of Galileo by the Catholic Church. The letters show developments in Descartes' construction and publication of the Discourse on Method, together with the essays Dioptrics, Meteors, and Geometry. This results in an explosion of letters from and to various critics such as the professor of medicine Vopiscus Fortunatus Plemp, the astrologer Jean Baptiste Morin, the mathematicians Pierre Petit, Gilles Personne de Roberval, Pierre de Fermat, and many others.