Behavioral couples therapy (BCT) sees the substance-abusing patient with the spouse to arrange a daily "sobriety contract" in which the patient states his or her intent not to drink or use drugs and the spouse expresses support for the patient's efforts to stay abstinent. BCT also teaches communication and increases positive activities. Research supports three conclusions. First, BCT for both alcoholism and drug abuse produces more abstinence and fewer substance-related problems, happier relationships, fewer couple separations and lower risk of divorce than does individual-based treatment. Second, domestic violence is substantially reduced after BCT for both alcoholism and drug abuse. Third, cost outcomes after BCT are very favorable for both alcoholism and drug abuse, and are superior to individual-based treatment for drug abuse. The Institute of Medicine (1998) documented a large gap between research and practice in substance abuse treatment. BCT is one example of this gap. BCT has relatively strong research support, but it has not yet become widely used.