Underage drinking is a significant problem in the United States: Alcohol is the primary contributor to the leading causes of death among adolescents. As a result, communitywide strategies to prevent underage drinking are more important than ever. Such strategies depend on the involvement and education of adolescents, parents, law enforcement officials, merchants, and other stakeholders. This guide is designed to take communities through the process of planning, implementing, and evaluating strategies to prevent underage drinking and youth access to alcohol. The guide is structured according to the Substance Abuse and Mental Health Services Administration’s (SAMHSA’s) Strategic Prevention Framework, a five-step prevention approach. Within the five steps, the guide adopts the Getting To Outcomes model of empowerment evaluation, results-based accountability, and continuous quality improvement. The result is a comprehensive, step-by-step manual for developing, implementing, and evaluating a high-quality communitywide plan to prevent underage drinking and its related consequences. Recommendations include the development of educational strategies for parents, adolescents, and alcohol merchants; attracting the involvement of civic leaders; working to reform legislation governing underage access to alcohol; and training law enforcement officials to be vigilant but safe in their efforts to police underage drinking in the community.