Results indicated that social capital was a significant predictor of substance use by high school students. Specifically, the greater social capital reported by high school students, the less likely they were to use illicit substances. This finding remained true for students in 9th through 12th grades. In particular, increased social capital was associated with decreased levels of alcohol use. Other findings revealed that as parental rules and expectations, human capital, and family climate increased among high school students, participation in substance use decreased. Taken together, the findings suggest that the development and maintenance of communication and social skills that foster relationships primarily with the family and secondarily with the school and community may be important in reducing substance use among adolescents. Future research should focus on the investigation of factors other than parental rules and expectations that are related to adolescent alcohol use. Participants were 590 high school students recruited from 2 public high schools in a medium-sized midwestern city. Participants completed self-report surveys that focused on substance use, risk factors, protective factors, parental rules and expectations, and indicators of human social capital, such as families’ level of engagement in educational and school-oriented behaviors, family climate, and family connectedness. Data were analyzed using multiple regression models. Table, references