In this article, the authors interrogate legal and economic history to analyze the process by which the Chicago School of Antitrust emerged in the 1950s and became dominant in the United States. They show that the extent to which economic objectives and theoretical views shaped the inception of antitrust law. After establishing the minor influence of economics in the promulgation of U.S. competition law, they highlight U.S. economists’ caution toward antitrust until the Second New Deal and analyze the process by which the Chicago School developed a general and coherent framework for competition policy. They rely mainly on the seminal and programmatic work of Director and Levi (1956) and trace how this theoretical paradigm became collective—that is, the “economization” process in U.S. antitrust. Finally, the authors discuss the implications and possible pitfalls of such a conversion to economics-led antitrust enforcement.