The authors assess gaps in the current knowledge base on psychotherapy research and the cost-effectiveness of psychotherapy. Despite the considerable and increasingly sophisticated body of research on the efficacy of psychotherapy, there is an alarming paucity of studies focusing on the cost-effectiveness of psychotherapy. This problem is particularly evident in the absence of studies exploring nonclinical effects of treatment and the broader range of domains in which intervention may have an impact. Initiation of research on the cost- effectiveness of psychotherapy is important for ensuring good clinical practice and data-based policy formulation. What is needed is greater specificity regarding the populations and problems for which psychotherapy can provide the greatest benefits, identification of the variables, measures, and methodological approaches that are most useful in yielding these important data, and comprehensive quantification of the costs and effects of psychotherapy.