In this talk, we examine the foundations ofMicroeconomic Theory froma differential viewpoint. First, we introduce the consumer problem and produce information about a given Economy by means of standard techniques in Differential Calculus. Then, we proceed to the analysis of the Theory of the Firm. Finally, the game-theoretical is examined, in the presence of a small number N of players. As N !1, the problem requires additional tools - from the realm of Analysis of Partial Differential Equations - and we grasp the surface of the beautiful theory behind such objects. Examples, counterexamples, anecdotes and some historical background permeates the talk. This is based on a Klein Project article, produced in collaboration with Lucas F. Lima (PPGM-UFSCar) and LuízaMonteiro (DEP-UFSCar).