In 1921, Etienne Gilson, one of the greatest Christian philosophers since Thomas Aquinas, began teaching at the Sorbonne. A twenty-three-year-old student, Henri Gouhier, promptly asked Gilson to direct his doctoral work on the great seventeenth-century philosopher Nicolas Malebranche. Gilson agreed. Thus began a relationship that ripened into a very deep personal and professional friendship lasting more than half a century. Gilson engaged in extensive correspondence throughout his long life, but little of it has seen the light of day. The letters in this volume, mostly from Gilson, reveal his extraordinary knowledge and intelligence, high standard of scholarship, sense of humor, remarkably distinctive style, and serious Catholicism. The letters also reveal aspects of Gilson the man behind the scholar hitherto privy only to students and close friends.