The Chicago School of antitrust has benefitted from a great deal of law office history, written by admiring advocates rather than more dispassionate observers. This essay attempts a more neutral examination of the ideology, political impulses, and economics that produced the School and that account for its durability. The origins of the Chicago School lie in a strong commitment to libertarianism and nonintervention. Economic models of perfect competition best suited these goals. The early strength of the Chicago School was that it provided simple, convincing answers to everything that was wrong with antitrust policy in the 1960s, when antitrust was characterized by over-enforcement, poor quality economics or none at all, and many internal contradictions. The Chicago School’s greatest weakness is that it did not keep up. Its leading advocates either spurned or ignored important developments in economics that gave a better accounting of an economy that was increasingly characterized by significant product differentiation, rapid innovation, networking, and strategic behavior. The Chicago School’s protest that newer models of the economy lacked testability lost its credibility as industrial economics experienced an empirical renaissance, nearly all of it based on models of imperfect competition. What kept Chicago alive was the financial support of firms and others who stood to profit from less intervention. Properly designed antitrust enforcement is a public good. Its beneficiaries—consumers—are individually small, numerous, scattered, and diverse. Those who stand to profit from nonintervention were fewer in number, individually much more powerful, and much more united in their message. As a result, the Chicago School went from being a model of enlightened economic policy to an economically outdated but nevertheless powerful tool of regulatory capture.