Martial Gueroult's Descartes selon I'ordre des raisons is one of the great works of Cartesian scholarship in the mid-twentieth century. Published in France in 1952 (a second edition appeared in 1968), Gueroult's commentary on Descartes philosophy has had a profound effect on French Cartesian studies, radically transforming the methodology for studying Descartes. Yet until now it has remained unavailable to English language readers, an absence due not only to its great length, but also to the tenor of modern Anglo-American Descartes studies. Though he is a pivotal figure in the history of philosophy, Descartes has often been the whipping boy of the Anglo-American analytic tradition; till recently, most writings about him were a historical commentaries set up to refute his ideas, or historical approaches that followed the order of topics and tended to considers each problem separately, a mode that Descartes explicitly rejected.