Bipolar I disorder (BP-I) is a chronic debilitating disorder with recurrent depressive and/or manic mood episodes. Although episodes of mania are often considered the most distinguishing feature of bipolar disorder, recurrent episodes of depression make up the most functionally debilitating aspect for many individuals with BP-I. Symptoms of depressive episodes include depressed mood, lack of interest, decreased energy, low self-esteem, trouble sleeping, and change in appetite. Mood stabilizers are usually the first line of treatment for patients with bipolar disorder who are in a depressive episode, but previous research has shown that these treatments fail to bring most patients to sustained remission. As an adjunct to medication, a psychosocial treatment known as cognitive behavioral therapy (CBT) may be a promising treatment for improving depressive symptoms and for long-term stabilization in individuals with BP-I. This study will compare the effectiveness of CBT versus supportive psychotherapy in decreasing depression in people with BP-I. Using magnetic resonance imaging (MRI), this study will also assess the impact of episodic memory impairment in people with BP-I on the success of CBT treatment.