Alan L. Smith, PhD, is associate professor of health and kinesiology at PurdueUniversity. He is recognized internationally for his research in developmental sport and exercise psychology, serves as associate editor of the Journal of Sport & ExercisePsychology, and is a consulting editor of Child Development. He is a fellow of the Research Consortium of the American Alliance for Health, Physical Education, Recreation and Dance and is a past chair of the SportPsychologyAcademy of the National Association for Sport and Physical Education. He earned his PhD in exercise and movement science from the University of Oregon. Stuart J. H. Biddle, PhD, is professor of exercise and sport psychology at LoughboroughUniversity. A recognized leader in the field of physical activity and health for young people, he has worked in the area for nearly 30 years. He is coauthor of the first textbook on exercise psychology and has delivered keynotes and other lectures in more than 20 countries. Dr. Biddle is past president of the European Federation for the Psychology of Sport and Physical Activity and was academic cochair of the Young and Active Project leading to national guidelines for physical activity for young people in the United Kingdom. He earned his PhD in psychology from KeeleUniversity.