Depression is one of the most common psychiatric disorders experienced by the older adults. The misconception that feeling sad is part of normal aging contributes to the underdiagnosis and undertreatment of depression in the older population. According to the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5), the category depressive disorders includes disruptive mood dysregulation disorder, major depressive disorder, persistent depressive disorder, premenstrual dysphoric disorder, substance-/medication-induced depressive disorder, depressive disorder due to another medical condition, and other specified depressive disorders and unspecified depressive disorders. The term late-life depression includes both older adults who are presenting with depression for the first time later in life (known as late-onset depression) and aging patients whose depressive disorders initially presented in earlier life. The following chapter presents an overview of the symptomatology, evaluation, and treatment of depression in the older population.