Abstract: This research evaluated the efficacy of a high-intensity social norms media marketing campaign aimed at correcting normative misperceptions and reducing the prevalence of drinking and driving among 21-to-34-year-olds in Montana. A quasi-experimental design was used, such that regions of Montana were assigned to one of three experimental groups: social norms media marketing campaign, buffer, and control. Four random samples of Montanans between the ages of 21 and 34 were assessed at four time points over 18†months via phone surveys. Findings suggest that the social norms media campaign was successful at exposing the targeted population to social norms messages in the counties within the intervention region. Moreover, results demonstrate the campaign reduced normative misperceptions, increased use of designated drivers, and decreased drinking and driving among those young adults in counties within the intervention region. Social norms media marketing can be effective at changing drinking-related behaviors at the population level. This research provides a model for utilizing social norms media marketing to address other behaviors related to public health.