What is needed for something new to appear? According to Gilles Deleuze, one of the most brilliant contemporary philosophers, this question of "novelty" is the major problem posed by Bergson's work. In this companion book to Bergson's Matter and Memory, Deleuze demonstrates both the development and the range of three fundamental Bergsonian concepts: duration, memory, and the élan vital. Bergsonism is also important to an understanding of Deleuze's own work, influenced as it is by Bergson.