Steven Nadler presents a biographical and philosophical study of Louis de La Forge (1632-1666), an important but underappreciated (and understudied) follower of René Descartes (1596-1650) who made a major contribution to making Cartesianism the dominant philosophical paradigm of the seventeenth century. La Forge was a devoted and faithful, but not uncritical, disciple who defended, updated, and even corrected Descartes' metaphysics, physics, and physiology, both to move Cartesian system to greater internal coherence and to make it more consistent with the latest scientific developments.