Cognitive behavioral therapy (CBT) is efficacious in the acute treatment of depression and may provide a viable alternative to antidepressant medication (ADM) for even more severely depressed unipolar patients when implemented in a competent fashion. CBT also may be of use as an adjunct to medication treatment of bipolar patients, although there have been few studies and they are not wholly consistent. CBT does seem to have an enduring effect that protects against subsequent relapse and recurrence following the end of active treatment, which is not the case for medications. Single studies that require replication suggest that patients who are married or unemployed or who have more antecedent life events may do better in CBT than in ADM, as might patients who are free from comorbid Axis II disorders, whereas patients with comorbid Axis II disorders seem to do better in ADM than in CBT. There also are indications that CBT may work through processes specified by theory to produce change in cognition that in turn mediate subsequent change in depression and freedom from relapse following treatment termination, although evidence in that regard is not yet conclusive.