AbstractRegulating private transactions across international boundaries has long posed a challenge to states. Extraterritoriality—the direct regulation of persons and conduct outside a state's borders—is an increasingly common mechanism by which strong states attempt to manage problems associated with transnational activities. This article seeks to account for variation across issues in the willingness of U.S. courts to regulate extraterritorially by focusing on the potential for external conduct to undermine domestic legal rules. It suggests further how attention to domestic-level regulatory processes, with particular focus on the role of private actors, can shed new light on transnational rulemaking and enforcement.