India’s urban slums exhibit dramatic variation in their levels of infrastructural development and access to public services. Why are some vulnerable communities able to demand and secure development from the state while others fail to? Based on ethnographic fieldwork and original household survey data, the author finds that party networks significantly influence the ability of poor urban communities to organize and demand development. In slums with dense party networks, competition among party workers generates a degree of accountability in local patron-client hierarchies that encourages development. Dense party networks also strengthen organizational capacity and provide settlements with vertical connectivity to politicians and officials. The presence of multiparty networks, however, may attenuate the positive influence of party network density. Interviews with political elites and the survey data suggest that politicians are less likely to provide services to slums with multiparty networks. From within settlements, partisan competition also creates perverse incentives for rival networks to undermine each other’s development efforts. This article contributes to scholarship on clientelism, which has overlooked variation in the density and partisan balance of patron-client networks across poor urban communities and the resulting divergences in democratic responsiveness and development that face those communities. It also contributes to research on distributive politics and the political economy of development.