What explains variation in neighborhood problem-solving? We argue that collective action infrastructure—place-based connections, organizations, knowledge, and practices formed while organizing—can reduce the costs of local collective action, even in communities without preexisting social and civic organizations. We adapt theories from the social movements literature about mobilizing structures and personal networks to the neighborhood context and propose that, even absent preexisting structures, an initial act of organizing in the face of a salient problem can itself facilitate future organizing. In contrast to expectations that local organizations will disband quickly upon achieving their initial goal, we argue that, because neighborhood problem-solving involves fixed costs and overlapping constituencies, local organizing infrastructure is often repurposable across issue areas. Observational data, a natural experiment, and a survey experiment from an online survey of residents across Mexico City demonstrate these downstream effects of organizing, even across unrelated issues.