This introductory chapter describes Chile’s recent and unprecedented wave of protests starting in late 2019 to situate this book within a broader socio-political context and academic debate. The book’s core contribution is the notion of mobilizational citizenship, which adds to the literature on social movements and citizenship studies. It explains how and why communities at the urban margins are able to sustain collective action over several decades and become prepared to support large-scale protests leading to a democratization process. To develop this theoretical argument, this book tells the story of two very similar urban communities founded in eastern Santiago in 1970. They have a similar socio-demographic configuration and location, their histories coincide, and grew as highly politicized and mobilized communities. Remarkably however, while one of the communities followed the pattern of demobilization observed across the country in the wake of its transition to democracy, the other is a counterexample of enduring mobilization. I studied this puzzling contrast through an ethnographic approach that included observations, interviews, and archival research.