This paper contributes to clarifying Deleuze’s theory of the Idea by a commentary on its technical definition: “a defined, continuous, n-dimensional multiplicity”, presented in chapter IV of Difference and Repetition. This definition implicitly intertwines Deleuze’s own metaphysical view of the Idea as a virtual problem with a series of notions taken from the differential geometry developed by the German mathematician Georg B. Riemann. To clarify this influence, we will reconstruct the fundamental elements of the Riemannian notions used by Deleuze, and (...) show how these elements are presupposed in Deleuze’s concept of Idea. (shrink)