Sedentary behavior is an important risk factor for chronic disease morbidity and mortality in aging. However, there is a limited amount of information on the type and amount of activity needed to promote optimal health and function in older people. The purpose of this review is to describe the change in patterns of habitual physical activity in aging and the relationship of these changes to physical function and selected chronic diseases. We undertook a literature review of large population-based studies of physical activity in older people, and there is encouraging evidence that moderate levels of physical activity may provide protection from certain chronic diseases. Additionally, substantial health effects can be accrued independent of the fitness effects achieved through sustained vigorous activity. Thus, regular participation (i.e., 30 minutes/day on most days of the week) in activities of moderate intensity (such as walking, climbing stairs, biking, or yardwork/gardening), which increase accumulated daily energy expenditure and maintain muscular strength, but may not be of sufficient intensity for improving fitness, should be encouraged in older adults. Public policy should focus on ways of increasing volitional and lifestyle activity in older people, as well as on increasing the availability and accessibility of senior and community center programs for promoting physical activity throughout the life span.