We live in an era where people live longer but also suffer from more chronic illnesses. Yet these two issues present not only significant challenges to healthcare professionals, but also governments seeking cost-effective ways to manage their health and social care budgets. Encouraging people to live healthier lifestyles is, therefore, a fundamental issue for both those at risk as well as for society as a whole. This is the first textbook to present not only the theoretical foundations that explain health behavior change but also the methods by which change can be assessed and the practical contexts where theory and method can be applied. Covering behavior change aimed at improving health as well as preventing disease, it places behavior change firmly in context with the social and demographic changes which make it such an urgent issue, from the rise in levels of obesity to an aging population. The book considers the role of individuals but also other important influences on health behavior, such as the environment in which people live, public policy and technological changes. Fostering a critical perspective, and including case studies in each chapter with key issues highlighted throughout, the book provides a complete understanding of health behavior change, from its theoretical building blocks to the practical challenges of developing and testing an intervention. It will be essential reading for students and researchers of health psychology, public health and social work, as well as any professional working in this important area.