Moderators are baseline variables that predict response to a treatment. Prognostic moderators predict response to all treatments, whereas prescriptive moderators predict differential response to particular treatments. In patients with major depressive disorder, prognostic variables include having anxious or chronic depression, living alone, and having psychiatric comorbidities. Prescriptive variables include gender, menopausal status, age and age at onset, depressive subtype, severity, and chronicity. Recognizing these variables can help clinicians better predict patients' response to treatment, select effective treatments for individual patients, and move patients to the next treatment step when response is inadequate. © Copyright 2011 Physicians Postgraduate Press, Inc.