We propose that social learning and social bonding theories are capable of account ing for the well-known relationship of crime and delinquency to age. Models incorporat ing age and variables derived from these two theories are tested with data on adolescent substance use among a large sample of Midwest adolescent s in Grades 7 through 12. Older adolescent s consume more marijuana than younger adolescent s, and the age–use curve is matched by the relationship between age and social learning variables. Di erences in use by age are also correlat ed with di erences in strength of social bonds by age, but to a lesser extent. The Žndings support the hypothesis that age variat ions in marijuana use are mediated by age-relat ed variat ions in social learning ; there is also support, although somewhat weaker, for the similar hypothesis that social bonding variables mediate the age–marijuana use relationship during adolescence.