Major depressive disorder is a serious form of depression that may be treated with psychotherapy. However, up to 40% of adults with depression do not show reduced symptoms when treated with cognitive therapy or behavioral activation (BA), two common forms of psychotherapy. Certain indicators are generally linked with a successful outcome of psychotherapy—demographic and clinical characteristics, comorbidity, and treatment adherence—but no factors reliably predict outcomes of psychotherapy in individuals. This study will test whether two characteristics related to the way people process emotions, affective asymmetry and affective reactivity, can predict whether people with depression will improve with BA therapy.