This article summarizes the proceedings of a symposium presented at the 2004 Research Society on Alcoholism meeting in Vancouver, British Columbia, organized by Alexander C. Wagenaar and chaired by Mark S. Goldman. The purpose of the symposium was to present the design and outcomes from a recently completed multi-community controlled time-series trial entitled Complying with the Minimum Drinking Age (CMDA), which tested two approaches for enhancing the effectiveness of the legal drinking age policy: training of alcohol retailers, and police enforcement at alcohol establishments. Specific presentations were: (1) Introduction and Overview of the CMDA project by Alexander C. Wagenaar, (2) CMDA Interventions by Traci L. Toomey, (3) CMDA Measurement, Statistical Methods and Results by Darin J. Erickson, and (4) Conclusions, Implications and Future Applications by Alexander C. Wagenaar. Results from the trial show: (1) minimal effects of the brief version of Alcohol Risk Management training for alcohol outlet management, (2) significant effects of enforcement checks in reducing sales of alcohol to youth, (3) a concentration of effects in specific alcohol outlets experiencing an enforcement check with little diffusion of effects to other outlets in the community not experiencing a check, and (4) a substantial decay of enforcement effects over the three months following a specific check. In short, results showed significant and substantial specific deterrence effects, and little training effects. Results also illustrated the utility and strength of the controlled time-series trial research design. Additional research on temporal and geospatial distribution of community-level intervention effects is warranted.