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 behaviour change but also the methods by which change can be assessed and the practical contexts where theory and method can be applied. Covering behaviour change aimed at improving health as well as preventing disease, it places behaviour 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.