<qa>  What is the first step toward the development and implementation of marijuana use preventionintervention programs?This study examines the impact of tailored computer-delivered and therapist-delivered brief motivations preventioninterventions both for adolescents who have not initiated marijuana use prevention, and those who use marijuana intervention. Key moderators of preventionintervention effectiveness will be examined, including behavioral intentions, self-efficacy, stage of change, school involvement, susceptibility to peer pressure, and potential health consequences such as STDHIV risk behaviors. This project will provide the critical first step toward the development and implementation of marijuana use preventionintervention programs that have the potential to be delivered to a large segment of youth who seek care in our nations primary care settings. 