Bipolar I disorder (BP-I) is a chronic disorder with recurrent depressed and/or manic mood episodes. Recurrent episodes of depression constitute the most functionally debilitating aspect for individuals with bipolar I disorder (BP-I). Mood stabilizers are the first line of treatment for patients with bipolar disorder in a depressive episode. However, these treatments fail to bring sustained remission for most patients. For example, despite the use of mood-stabilizing agents, longitudinal data suggests relapse rates as high as 40% in one year, 60% in two years, and 73% in five or more years. Thus, despite advances in the pharmacologic treatment of bipolar disorder, it has become clear that additional strategies are needed to provide patients with longer-term mood stability. Cognitive-Behavior Therapy (CBT) has been shown to enhance medication compliance as well as to reduce rates of relapses in patients with bipolar disorder. Although there is substantial evidence that CBT is an effective treatment for depressive episodes in major depression, surprisingly few studies have investigated the efficacy of CBT for depressive episodes in bipolar disorder. In addition, existing CBT studies suffer from several short-comings including small sample sizes, the lack of control groups and active control treatments. The present application addresses this gap by proposing to conduct a randomized controlled treatment trial of CBT compared to supportive psychotherapy (the most widely available type of psychotherapy in the community) in depressed patients with bipolar I disorder and to investigate moderators and mediators of treatment response to CBT.