Late life depression is a significant public health problem as well as a burden on patients, their families, and caregivers. There are significant associations of late life depression with medical disorders and cognitive impairment, the latter due to effects of the depression itself or association with dementia. Diagnostic criteria and screening tests have continued to evolve and provide structure and guidelines for assessment. Accurate diagnosis and treatment are of utmost importance to improve quality of life, alleviate suffering, and prevent suicide. A number of effective antidepressant medications are available; combination therapy with these medications and cognitive behavioral therapy appear most efficacious, and maintenance therapy can decrease the chances of remission. A sequence for treatment of late life depression is provided, with strategies for treatment-resistant depression. The relationship of dementia to depression and the interaction of depression with mechanisms of aging are major foci of research.