This Article discusses the role of U.S. citizenship in determining who would be protected by the Constitution, other domestic laws, and the courts. Traditionally, within the United States, both noncitizens and citizens have had more or less equal civil liberties protections. But outside the sovereign territory of the United States, noncitizens have historically lacked such protections. This Article sketches the traditional rules that demarcated the boundaries of protection, then addresses the functional and normative justifications for the very different treatment of noncitizens depending on whether or not they were present within the United States.