Although Robert Klein (1918–1967), well known for his erudition and the originality of his research, was an important, even paradigmatic figure for the field of art history in the twentieth century, no sustained study has yet been dedicated to his work. Klein undertook to rethink Renaissance art and its history from the Aristotelian notion of technē as early as the 1950s, long before anyone was interested in this other genealogy of Renaissance art. For him, the Mannerist work is intended to create awe and wonder, inviting the viewer to question the technical process, a combination of intelligence and manual skill, that made it possible to realize in this specific form. As his newly discovered papers and unpublished manuscripts testify, technē and Mannerism are far from being Klein’s only preoccupations. Other concepts have been studied with great originality by Klein, such as mnemonic art, paragone, dream, and responsibility. This book, proceeding from a conference organized by Villa I Tatti, Kunsthistorisches Institut in Florence, and the Institut national d’histoire de l’art (INHA) in Paris, sheds light on Klein’s investigations as well as on the intellectual journey of an important art historian and philosopher of the past century.