This dissertation examines the use of coordinated multistate lawsuits by state attorneys general (SAGs) as a tool to create national policy. Entrepreneurial SAGs have increasingly employed multistate litigation against private industry and the federal government, reaching numerous out-of-court settlements and favorable court judgments. These lawsuits have imposed new national regulatory requirements across several policy areas and have challenged regulatory regimes established by Congress and federal agencies. This study investigates three interrelated questions about multistate SAG litigation: (1) how SAGs have used this litigation to achieve national regulatory goals, (2) why this activity has increased over time, and (3) what the consequences are for American politics and policy. Employing both qualitative and quantitative analysis, I examine these questions through two stages. First, I present an analysis of an original dataset containing SAG lawsuits and legal settlements in four key policy areas covering 1980 through 2009. Second, I examine three case studies involving pharmaceutical litigation, air pollution control litigation, and lawsuits against the firearms industry. I find that changes in federal law instituted by Congress and the federal courts have created new opportunity points for SAGs, helping spur a dramatic increase of multistate litigation. The SAGs built upon earlier successful efforts, including their blockbuster settlement with the tobacco industry in 1998, to create new avenues of collaboration among their fellow SAGs, public interest groups, and the private bar. The result has been to substantially alter the regulatory landscape in areas including prescription drug pricing, pharmaceutical advertising, and greenhouse gas emissions. By shedding light on this significant form of "regulation through litigation," this dissertation illustrates how SAGs have seized upon the trend towards adversarial legalism in America by using the courts to achieve policy goals when attempts to do so in other venues fail. This runs contrary to a line of scholarly literature suggesting that litigation and courts have a limited impact on significant social change. This study also demonstrates how American federalism, commonly thought to serve as a restraint on the federal government by diffusing power, can be used by skillful political actors to create more energetic government and stronger national regulation.