This article investigates the history of the Progressive Era effort to develop new techniques and technologies of control over American business and corporations in the late nineteenth and early twentieth centuries. A revolution in Progressive economic regulation was rooted in the intellectual work of the so-called institutional economists—particularly in the context of what economists and lawyers like Richard Ely, John Commons, and Walton Hamilton ultimately talked about as the movement for the “social control” of business, with distinct emphasis on the legal and regulatory “foundations” of modern capitalism. With increased attention to dynamics rather than statics, the real social economy rather than ideal rational actors, and historical and institutional rather than theoretical and abstract renderings of business, industry, and the market, the institutionalists were directly concerned with problems of control, particularly those mechanisms of control available through law, politics, the state, and new technologies of legislative and administrative regulation.