Health-related problems are strongly associated with the social characteristics of communities and neighborhoods. We need to treat community contexts as important units of analysis in their own right, which in turn calls for new measurement strategies as well as theoretical frameworks that do not simply treat the neighborhood as a "trait" of the individual. Recent findings from the Project on Human Development in Chicago Neighborhoods support this thesis. Two major themes merit special attention: (1) the importance of collective efficacy for understanding health disparities in the modern city; and (2) the salience of spatial dynamics that go beyond the confines of local neighborhoods. Further efforts to explain the causes of variation in collective processes associated with healthy communities may provide innovative opportunities for preventive intervention.