In this chapter, Jessica M. Mulligan and Heide Castañeda provide an overview of the Affordable Care Act focused on the coverage expansions that were at the heart of the law. The authors outline the ethnographic methods used in the book, arguing that an anthropological approach provides an experience-near perspective on implementation that too often is absent in mainstream treatments of health policy. The central theoretical concerns of the book are also introduced: stratified citizenship, risk, and responsibility. The term stratified citizenship describes how certain social identities and demographic characteristics—such as immigration status, income, gender, race, and state of residence—mediated how people were included or excluded from health insurance coverage through the ACA. Exposure to risks as well as inclusion in the new responsibilities created by the law were also unequally distributed.