Theory: Social capital is the web of cooperative relationships between citizens that facilitates resolution of collection action problems (Coleman 1990; Putnam 1993). Although normally conceived as a property of communities, the reciprocal relationship between community involvement and trust in others is a demonstration of social capital in individual behavior and attitudes. Hypotheses: Variation in social capital can be explained by citizens' psychological involvement with their communities, cognitive abilities, economic resources, and general life satisfaction. This variation affects citizens' confidence in national institutions, beyond specific controls for measures of actual performance. Methods: We analyze the pooled General Social Surveys from 1972 to 1994 in a latent variables framework incorporating aggregate contextual data. Results: Civic engagement and interpersonal trust are in a tight reciprocal relationship, where the connection is stronger from participation to interpersonal trust, rather than the reverse.