The benefits of physical activity for adults are well established, but less than one-third of older adults in the U.S. have achieved recommended levels of physical activity despite widespread clinical recommendations to increase physical activity in recent years. Clinic-based approaches to increasing physical activity are expensive, difficult to implement in busy practice settings, and have limited reach. Moreover, evidence of the efficacy of such approaches is equivocal. A population based approach may be a more effective and less costly strategy to increase levels of physical activity in older adults. Population studies of physical activity have demonstrated that each year, many sedentary older adults initiate physical activity, but a nearly equal number of those who were active become sedentary. Among older adults initiating physical activity, only half continue to be active 3 months later.