Physical inactivity is a major public health problem, and compelling evidence suggests that it is a contributing factor in several chronic diseases and conditions. Recognition of the health and functional hazards of a sedentary way of life has led numerous groups to promulgate public health recommendations for physical activity. In this report, we review the evolution of physical activity recommendations, discuss reasons for differences in the recommendations, and provide a summary recommendation in an attempt to harmonize existing differences. Current public health recommendations for physical activity are for 30 min of moderate-intensity activity each day, which provides substantial benefits across a broad range of health outcomes for sedentary adults. This dose of exercise may be insufficient to prevent unhealthful weight gain for some persons who may need additional exercise or caloric restriction to minimize the likelihood of further weight gain. Persons who get 30 min of moderate-intensity exercise per day are likely to achieve additional health benefits if they exercise more. In addition to aerobic exercise, people should engage in resistance training and flexibility exercises at least twice a week, which will promote the maintenance of lean body mass, improvements in muscular strength and endurance, and preservation of function, all of which enable long-term participation in regular physical activity and promote quality of life.