Concepts representing the context of marijuana initiation included attachment to parents and peers, exposure to drug- related attitudes of parents and peers, peer behavior, and the decisionmaking process involving expected costs and benefits of marijuana use. Measures representing these concepts were included in logistic regression models to predict marijuana initiation. Regression parameters were compared for students in the sixth, seventh, and eighth grades. Findings demonstrated that only parental attachment measures influenced marijuana initiation for the youngest group. A mix of parental and peer attachment and peer exposure measures affected marijuana initiation for the middle group, and only measures of peer attachment and exposure and the relative importance of marijuana use costs predicted initiation for the oldest group. Results suggest that developmental factors influence the context of marijuana initiation. Therefore, it is not appropriate to view adolescents as a single group when attempting to understand their drug use behavior. 42 references, 1 note, and 4 tables