Since the release of, “Physical Activity and Health: A Report of the Surgeon General” in 1996, the science base on the health benefits of physical activity has continued to strengthen. Consequently, the U.S. Department of Health and Human Services (HHS) considered whether a national set of physical activity guidelines was appropriate. With the help of the Institute of Medicine, HHS convened a workshop in October 2006 to address this question. The workshop's report, Adequacy of Evidence for Physical Activity Guidelines Development, affirmed that advances in the science of physical activity and health justified the creation of the physical activity guidelines. The developmental process of the Physical Activity Guidelines for Americans was similar to that used for the Dietary Guidelines for Americans. In 2007, HHS Secretary Mike Leavitt appointed an external scientific advisory committee, called the Physical Activity Guidelines Advisory Committee. The Physical Activity Guidelines Advisory Committee Report, 2008 and meeting summaries are available at http://www.health.gov/PAGuidelines/. The document Physical Activity Guidelines for Americans describes the major research findings on the health benefits of physical activity: Regular physical activity reduces the risk of many adverse health outcomes. Some physical activity is better than none. For most health outcomes, additional benefits occur as the amount of physical activity increases through higher intensity, greater frequency, and/or longer duration. Most health benefits occur with at least 150 minutes (2 hours and 30 minutes) a week of moderate-intensity physical activity, such as brisk walking. Additional benefits occur with more physical activity. Both aerobic (endurance) and muscle-strengthening (resistance) physical activity are beneficial. Health benefits occur for children and adolescents, young and middle-aged adults, older adults, and those in every studied racial and ethnic group. The health benefits of physical activity occur for people with disabilities and the benefits of physical activity far outweigh the possibility of adverse outcomes. The Guidelines provide key guidance for specific population subgroups. This includes specific guidelines for: children and adolescents; adults (ages 18-64 years); older adults (ages 65 years and older); women during pregnancy and the postpartum period; adults with disabilities; and people with chronic medical conditions (e.g., coronary heart disease, stroke, type 2 diabetes mellitus, hypertension, selected cancers). Finally, the Guidelines provides guidance for engaging in safe physical activity across the lifecycle. Keyword(s): research