Deleuze has had a profound impact on contemporary approaches to the theory of power. Through his studies of the philosophies of Nietzsche and Spinoza, he develops a concept of power which has none of the juridical and moral presuppositions typically associated with power in the tradition of modern political thought. This concept of power none the less enables a form of ethical evaluation which plays an important role in the social and political theory developed in collaboration with Guattari. It informs both the theory of desire that is the basis for their critique of psychoanalysis in Anti-Oedipus (1977) and the theory of assemblages developed in A Thousand Plateaus (1987). The key elements of Deleuze’s concept of power are presented in his 1962 study, Nietzsche and Philosophy (1983). The aim of this chapter is to outline the concept of power developed through Deleuze’s interpretation of Nietzsche, and to show how this is developed further in his subsequent collaboration with Guattari.