The Community Intervention Trial for Smoking Cessation (COMMIT) is a multicenter project created to test a comprehensive smoking control intervention. COMMIT was designed to effectively reach cigarette smokers, especially heavy smokers, and to aid them in achieving and maintaining long-term cessation of cigarette smoking. COMMIT was also designed to work through communities, using existing media channels, major organizations, and social institutions capable of influencing smoking behavior in large groups of people. This ongoing trial was begun in 1989 in 11 matched pairs of communities. Each pair consists of one community randomized to intervention conditions and one community randomized to comparison conditions. A comprehensive set of mandated activities is organized around four task forces encompassing health care providers, work sites and organizations, cessation resources and services, and public education. Intervention activities are adapted and implemented in each community through a local community board that provides oversight and management of COMMIT activities. Cessation rates will be assessed in randomly selected cohorts of heavy cigarette smokers, identified at the baseline survey and tracked for 5 years, as estimators of the overall quit rates in both intervention and comparison communities. Various data collection methods will be used to provide intermediate outcome measurement and to evaluate implementation. These methods include cross-sectional community surveys and surveys of health providers, work sites, religious organizations, cessation resource providers, and other systems used to track smoking control activities. The trial will have an impact on more than 200 000 adult smokers. [J Natl Cancer Inst 83:1620–1628, 1991]