Grassroots Power reveals how ordinary voters harness their collective political power through bloc voting, using community organizing to strengthen local democracy. The book counters stereotypes of disengaged or coerced voters and instead demonstrates how community associations shift power dynamics between marginalized residents and politicians in rural Northeast Brazil. The book introduces the framework of grassroots bloc voting, where residents mobilize their bottom-up community organizing around essential services like water. While this strategy yields lasting improvements in water services, those unable to coordinate are further left behind. Combining extensive fieldwork, original surveys, localized polling data, novel survey experiments, and social media data, Grassroots Power provides an evidence-based framework for how vulnerable populations defy political coercion and strengthen local democracy from the ground up.