In North America, 40-50 per cent of older adults are actively involved as formal volunteers in providing diverse health and human services. We review empirical studies concerning older adults' motivations for volunteering, as well as the health and morale benefits they derive from this expression of altruism. Knowledge of the exact nature and amount of volunteer activity necessary to produce these effects is limited, and studies have yet to identify the behavioural and psychological mechanisms that are implicated. We propose that older adult volunteers may enjoy good health and longevity because being useful to others instills a sense of being needed and valued. We present several theoretical perspectives on the developmental significance of volunteering, discuss the challenges to volunteerism imposed by the baby boom cohort, and identify future research priorities.