The paper traces the genealogy of social and legal inequalities in citizenship and in the racialization of immigrants in the U.S. that are constitutive of contemporary immigrant detention practices. Presenting a challenge to the exceptionalism which frames policy responses to 9/11 and the “war on terror,” the paper argues that contemporary detention policies emerge from an episodic history of immigrant detention, precipitated by a series of broadly defined national security crises over the last century—from fear of contagion, to the demonization of “foreign” ideologies, to international military conflicts and domestic “wars” on crime, drugs and terrorism. These “crises” have been invoked to reduce the rights and civil liberties of racialized immigrants and citizens in the detention process. Even before the “war on terror” began, the coordinates of race, noncitizenship and national crisis were mobilized by the government through the vehicle of detention to deny due procedural rights to racialized immigrants. Such policies, often practiced legally and extralegally, serve to highlight the broad formation of a near permanent lesser class of persons vulnerable to institutionalized inequalities in the United States.