This book is a philosophical study of the concept of affect in the thought of Henri Bergson. It provides an account of the place and evolution of the idea throughout Bergson's works and argues that an understanding of the changing nature of this central concept reveals important ruptures in Bergson's own philosophical development. As Bergson shows, affectivity plays a central role in philosophical thinking about consciousness. In his early work, Bergson's describes an embodied, temporal subject whose very subjectivity relies on a productive notion of affectivity. As his thought develops, however, Bergson's metaphysics take an increasingly utilitarian turn characterized by the minimization of affectivity. Through a series of transformations, disappearances, and displacements, affectivity comes to qualify the way Bergson understands everything from the body, to subjectivity, to life as such. The book concludes by discussing the pivotal role these ideas played in how Bergson was received by 20th Century phenomenology.