The National Institute on Drug Abuse Collaborative Cocaine Treatment Study is a large, multisite psychotherapy clinical trial for outpatients who meet the DSM-IV criteria for cocaine dependence. For 480 randomized patients, the outcomes of 4 treatments are compared for an 18-month period. All treatments include group drug counseling. One treatment also adds cognitive therapy, one adds supportive-expressive psychodynamic therapy, and one adds individual drug counseling; one consists of group drug counseling alone. In addition, 2 specific interaction hypotheses, one involving psychiatric severity and the other involving degree of antisocial personality characteristics, are being tested. This article describes the main aims of the project, the background and rationale for the study design, the rationale for the choice of treatments and patient population, and a brief description of the research plan.