Problems of alcohol and drug dependence are costly to society in terms of lost productivity, social disorder, and avoidable health care utilization. The dollar costs of alcohol and drug use run into billions of dollars, and from one-eighth to one-sixth of all deaths can be traced to this source. However, the efficacy of treatment for addiction is often questioned. A rationale for reasonable expectations of addiction treatments is offered, from which are derived three outcome criteria for judging the effectiveness of treatments: reduction in substance use; improvement in personal health and social function; and reduction in public health and safety risks. Based on these criteria, treatment was shown to be effective, especially when compared with alternatives like no treatment or incarceration. These evaluations, which were conducted in a scientific manner, support the continued value of public spending for carefully monitored treatment of addiction.