This paper provides an in-depth analysis of Deleuze's interpretation of Bergson, based on his largely ignored 1956 essay, "Mergson's Conception of Difference." In this essay, Deleuze first attacks the Hegelian tradition for misunderstanding the notion of difference by reducing it to negation and then uses Bergson's concept of duration – a flow of purely qualitative mental states – to formulate a notion of difference utterly "internal" to itself, that is, irreducible to negation. The paper argues that this temporalization of difference represents a permanent feature of Deleuze's philosophy – one particularly visible in his highly influential book on Nietzsche – and concludes that Deleuze's Nietzsche therefore appears molded by a Bergsonian imprint.