 The purpose of this study is to compare the effectiveness of two different augmentation strategies of antidepressant treatment for depressed older adults who have not responded to an adequate trial of antidepressant medication. The first augmentation strategy is Problem Solving Therapy PST, a 12-week psychotherapy treatment that has been shown to be effective in depressed older adults. The second augmentation strategy is medication augmentation, which will begin with six weeks of aripiprazole, an atypical antipsychotic medication that has also been shown to be effective in depressed older adults who have failed a trial of antidepressant medication. 