Amid contentious debates about citizenship, borders, and belonging, naturalization tends to stand apart, widely celebrated as the culmination of immigrant narratives and American ideals of liberalism. In Naturalization, Siobhan B. Somerville unsettles this story, showing how the process of citizen-making has historically been embedded in normative assumptions about race, indigeneity, and sexuality that have sustained the US settler colonial project. Tracing an alternative genealogy of naturalization from the eighteenth century through the mid-twentieth, Somerville investigates overlooked stories not only of immigrants but also of Indigenous people, formerly enslaved people of African descent, and inhabitants of US territories, many of whom became US citizens through collective naturalization, often without their consent. Somerville’s interdisciplinary approach to a wide-ranging archive—including federal law, photographs, letters, and memoirs—shows how naturalization has long functioned as both a powerful metaphor and a contradictory material practice at the core of the US settler colonial state.