Optimising happiness is a desirable societal aim in itself, but there are four more specific reasons why research on happiness is an important emerging theme in gerontology. First, happiness is not merely the mirror of depression, anxiety or distress, but has distinct relationships with a range of outcomes, so benefits from study in itself. Second, happiness appears to be a protective factor for morbidity and mortality; although studies are complex and take a long time to complete, there is accumulating evidence that greater happiness predicts survival among older people independently of covariates including health status and depression. Third, happiness has broad ramifications at older ages, being related to personal and social relationships, economic prosperity, biological risk factors, health behaviours, and time use as well as health. Fourth, happiness is malleable, and can potentially be modified in ways that will enhance the health and well-being of older people.