In elderly people, depression mainly affects those with chronic medical illnesses and cognitive impairment, causes suffering, family disruption, and disability, worsens the outcomes of many medical illnesses, and increases mortality. Ageing-related and disease-related processes, including arteriosclerosis and inflammatory, endocrine, and immune changes compromise the integrity of frontostriatal pathways, the amygdala, and the hippocampus, and increase vulnerability to depression. Heredity factors might also play a part. Psychosocial adversity-economic impoverishment, disability, isolation, relocation, caregiving, and bereavement-contributes to physiological changes, further increasing susceptibility to depression or triggering depression in already vulnerable elderly individuals. Treatment with antidepressants is well tolerated by elderly people and is, overall, as effective as in young adults. Evidence-based guidelines for prevention of new episodes of depression are available as are care-delivery systems that increase the likelihood of diagnosis, and improve the treatment of, late-life depression. However, in North America at least, public insurance covers these services inadequately.