Prosociality, conceptualized as a willingness to help, to be fair, and to be friendly to others, is essential to the maintenance of a civil society and has been linked with multiple measures of individual well-being. This study examines how individual, family, and neighborhood factors affect adolescents' level of prosociality and tests for moderating influences in these relationships. Data for this study come from the 12-year-old cohort of the Project on Human Development in Chicago Neighborhoods (PHDCN) study (N = 723). Results show that being female and having the ability to rely on family, a teacher/coach, or an adult in the community predicts significantly higher levels of prosociality. In addition, I find that neighborhood collective efficacy moderates the relationship between gender and prosociality, serving as a protective factor in the development of prosociality for boys. The findings of this study are discussed in the context of a sociological view of positive youth development.