This article describes the assertive community treatment model of comprehensive community-based psychiatric care for persons with severe mental illness and discusses issues pertaining to implementation of the model. The assertive community treatment model has been the subject of more than 25 randomized controlled trials. Research has shown that this type of program is effective in reducing hospitalization, is more expensive than traditional care, and is more satisfactory to consumers and their families than standard care. Despite evidence of the efficacy of assertive community treatment, it is not uniformly available to the individuals who might benefit from it. (Authors)