We examine the rise of the US regulatory state with a specific focus on regulations that arose during the Progressive Era, the period during which state and federal governments became dominant actors in regulating economic activity. Our analysis highlights four key themes in the rise of regulation in America. The first is how a major shift in the structure of government during the mid nineteenth century preceded the rise of regulation at the state and federal levels. The second is how the forces of specialization created an environment conducive to the emergence of regulation. The third deals with the path-dependent nature of regulation. The final theme concerns the federal nature of the American political system and its implications for the rise of regulation.