We studied patterns and levels of enforcement of the legal drinking age in the United States. Major findings include: (1) rates of enforcement of the legal drinking age are very low; (2) actions against outlets or adults providing alcohol to youth are particularly rare; (3) two of every thousand occasions of illegal drinking by youth under 21 are estimated to result in an arrest; (4) five of every 100,000 youth drinking occasions are estimated to result in an Alcohol Beverage Control agency action against an alcohol outlet; (5) penalties appear too lenient to deter providers of alcohol; and (6) levels of enforcement of the drinking age vary significantly across states. Recommendations for public policy and enforcement actions include: (1) increased enforcement effort be directed at those who provide alcohol to underage youth; (2) significant increases in the numbers of Alcohol Beverage Control enforcement personnel are needed; (3) one or more officers in each local enforcement agency should be designated as the alcohol control officer; (4) regular sting operations in retail alcohol outlets are needed; (5) all police-attended alcohol-involved incidents should include a record of the source of the alcohol; and (6) effective long-term efforts will require attention to the broader environment that encourages youth drinking.