This essay argues that Guantánamo lies at the heart of the American Empire. The legal status of the prisoners there must be understood in the context of an imperial history that dates back to the U.S. occupation of Cuba in 1898. This history explains how the U.S. Naval Station, Guantánamo Bay, Cuba, has become an ambiguous space, both inside and outside national and juridical borders and how this ambiguity reinforces the harsh penal regime. The essay argues that the legacies of U.S. imperialism inform key contemporary debates about Guantánamo: the question of national sovereignty, the codification of the prisoners as "enemy combatants," and the uncertainty about whether the U.S. Constitution holds sway there. Turning to the 2004 Supreme Court decision, Rasul v. Bush, the essay argues that the justices are not only interested in restraining executive power to bring Guantánamo within the rule of domestic law; they also show concern with the scope of U.S. power in the world and the extent to which the judiciary should accompany or limit U.S. military rule abroad. A close reading of the Supreme Court's decision and dissent shows that the logic and rhetoric of Rasul v. Bush rely on and perpetuate the imperial history the decision also elides. In concert other recent decisions about civil liberties and national security, Rasul v. Bush contributes to the global expansion of U.S. power by reworking the earlier history of imperial rule. The Court's legal decisions respond to the changing demands of empire today by creating new categories of persons before the law that extend far beyond Guantánamo Bay, Cuba.