Multiple personal, environmental, and behavioral factors influence participation in lifestyle physical activity and exercise. Psychosocial influences are those psychological and social factors that are associated with physical activity behavior change and maintenance. Increasing and sustaining physically active lifestyles are important public health issues given the health risks associated with inactivity and the growing obesity epidemic. Psychosocial factors have been studied for decades with the hope of explaining, predicting, and modifying levels of physical activity. This entry begins with a discussion of moderators and mediators of behavior change to set the stage for understanding the relationship between psychosocial factors and behavior. Next, the psychosocial constructs that influence physical activity and exercise are described. The entry concludes with a discussion of less established but promising constructs and ...