This is a pilot study of the effectiveness of adding Abilify (aripiprazole), an atypical antipsychotic medication, to ongoing selective serotonin reuptake inhibitor (SSRI) antidepressant treatment for depressed outpatients who are not responding fully to SSRI treatment alone. Fifteen subjects will be given aripiprazole in a flexible dosing schedule and followed for 12 weeks, while continuing their ongoing SSRI medication. Assessments of depressive symptoms, overall functioning, social functioning, and side effects will be completed. It is hypothesized that patients' functioning will improve after 12 weeks of treatment with Aripiprazole and SSRI medication.