In this article, old age is defined as 65 years and upwards, and late life as 85 years and over. Depression is extremely common in older people. Its aetiology is complex, with particular age-related factors of physical comorbidity, polypharmacy and declining social activity. There is also overlap with dementia, although the nature of the relationship is unclear. Assessment is problematic as symptoms may be masked or mistaken for other pathology, justifying use of specific instruments for diagnosing depression in older people. Treatment options are discussed, with due consideration of side-effects. Bespoke care management is emphasised, with a positive message that depression in old age is a treatable condition.