This monograph, Theory at a Glance: Application to Health Promotion and Health Behavior (Second Edition), describes influential theories of health-related behaviors, processes of shaping behavior, and the effects of community and environmental factors on behavior. It complements existing resources that offer tools, techniques, and model programs for practice, such as Making Health Communication Programs Work: A Planner's Guide, i and the Web portal, Cancer Control PLANET (Plan, Link, Act, Network with Evidence-based Tools).ii Theory at a Glance makes health behavior theory accessible and provides tools to solve problems and assess the effectiveness of health promotion programs. (For the purposes of this monograph, health promotion is broadly defined as the process of enabling people to increase control over, and to improve, their health. Thus, the focus goes beyond traditional primary and secondary prevention programs.