Who qualifies, with full status, as an American citizen? Like all modern nation-states, the United States erects and maintains various types of legal and geographic boundaries to demarcate citizens from noncitizens. The literature in political science tends to focus on the ways in which immigration law structures citizenship over time, but this is only half the story. As this dissertation demonstrates, governments also regulate the birth of citizens from one generation to the next. The concept of a ‘civic lineage regime’ is introduced as the domestic counterpart to the ‘immigration regime,’ when it comes to structuring civic membership in the United States (and other nations). To bring visibility to this deeply constitutive yet largely unexamined dimension of American political development, the project engages in a close analysis of U.S. Supreme Court cases targeting civic lineage during the twentieth century. Examining eugenic sterilization laws, birth control, abortion, and welfare reform, the dissertation maintains that the federal and state governments regulate the intimate lives of Americans for many of the same reasons governments seek to control immigration. In both realms, the state makes legal distinctions between who can and cannot become a member by coercively privileging certain visions of American identity over others. This often entrenches hierarchies of citizenship based on race, gender, ethnicity, class, disability, religion, and sexuality. These state-building policies, involving the regulation of reproduction and birth, have the ability to define and redefine the meaning and scope of U.S. citizenship across time by shaping the future “face” of the American polity. Finally, although many older inegalitarian conceptions of civic membership are now discredited, the dissertation concludes with evidence that the conflictual politics involved in constructing an American civic lineage regime continue today in the form of the rise of a new ‘neoliberal ideal of citizenship.’