This chapter analyses the Marginalist Revolution started in the 1870s by Jevons, Walras, and Menger – which shifted the foundations of economic value from the Classical labour theory to subjective marginal utility. This transition marked the ascent of microeconomic analysis aiming to become hegemonic within economics. It contrasts Smith’s framework based on sympathy (in The Theory of Moral Sentiments) with the focus on self-interest (in The Wealth of Nations). This shift reflects the ongoing evolution from personal community relations influenced by sympathy to impersonal market interactions mediated by competition. Bentham and Mill played crucial roles in transforming traditional utilitarianism into an operational decision theory, Jevons explicitly aimed to create a ‘calculus of Pleasure and Pain’, using marginal utility to explain exchange value and relative prices, viewing production costs as determined by value. Walras extended this approach by developing the first general equilibrium model, representing the interdependence of all markets. Menger provided an approach to the foundations based on methodological individualism. Despite the alleged unification of value theory under utility, the Marginalist Revolution faced several challenges, including the difficulty of comparing the utility of individuals. Its initial impact was thus limited, paving the way for the hegemony of the Marshallian Synthesis.