Depression affects 6.5 million of the 35 million Americans ≥65 years of age. While depression usually begins earlier in life and recurs periodically, it can present for the first time in people 80–90 years of age as well. Depression throughout the lifespan has a genetic/biological component but is also very much affected by social environmental factors. As people age, demographic factors, social support, and negative life events remain important to overall mental health, while physical illness and disability begin to take on a much more prominent role. Depression in the elderly is associated with impairment, dependency, disability, and significant distress for the individual and their family. This population is likely to present with concomitant cognitive dysfunction and medical illness, which can complicate the identification and treatment of psychiatric conditions. Bereavement is almost universal in late life and is sometimes a deterrent to appropriate diagnosis and treatment of depression. Physical frailty and diminishing social resources further complicate the treatment of depression in the elderly. Elderly individuals respond well to standard pharmacotherapy and psychotherapy treatments for depression. However, due to the high rate of relapse of depression in this population, continuous treatment is often warranted. This monograph will review depression in the elderly in the context of social disruptions, such as bereavement, caregiver strain, interpersonal conflict, role transitions, and social isolation; late-onset vascular depression and cognitive impairment; and physical illness including disability.