This article includes an historical review of research on physical activity and health, and how the findings have contributed to physical activity participation and promotion today. In the 20th century, research began to accumulate on the effects of exercise on physiological functions, and later on the relation between regular activity and various health outcomes. In the latter half of the 20th century, it became clear that physical inactivity is one of the major public health problems in the world. This prompted numerous organizations and governments to issue recommendations for increasing physical activity in the population. The United States now has official governmental guidelines for physical activity. In addition, numerous public and private organizations have collaborated to develop and implement a U.S. National Physical Activity Plan.