 While René Descartes (1596–1650) is well-known as one of the founders of modern philosophy, his influential role in the development of modern physics has been, until the later half of the twentieth century, generally under-appreciated and under-investigated by both historians and philosophers of science. Not only did Descartes provide the first distinctly modern formulation of laws of nature and a conservation principle of motion, but he also constructed what would become the most popular theory of planetary motion of the late seventeenth century. As the renowned historian of science Clifford Truesdell has observed, “[Descartes’ physics] is the beginning of theory in the modern sense” (Truesdell 1984, 6). Yet, for all of the forward-looking, seemingly modern, aspects of Descartes’ physics, many of Descartes’ physical hypotheses bear a close kinship with the Aristotelian-influenced science of late-Medieval and Renaissance Scholasticism. It is this unique amalgam of both old and new concepts of the physical world that may account for the current revival of scholarly interest in Descartes’ physics.