Objectives: To describe distribution of obesity and it trend by socio-demographic (age, gender, region) and socio-economic status (education level, social class) in England and Scotland. To review the relationship between obesity and all causes, coronary heart disease, stroke, hypertension, cancer, asthma, diabetes, osteoarthritis and thyroid disorders. To assess the economic consequences of obesity. To evaluate the cost-effectiveness of interventions for prevention of obesity in adults. Methods: A series of Systematic reviews conducted as well as statistical analysis of the UK Archive and Grampian Health Board data. Results: Health Surveys for England, Scottish Health Surveys and Grampian Lifestyle Surveys show that obesity and overweight are increasing across all socio-economic and demographic groups. The nature of the relationships between obesity and CHD, stroke, hypertension, cancer, diabetes, osteoarthritis, thyroid disorders, asthma and excess of all causes mortality are analysed and discussed. The huge economic burden of obesity (up to 8 percent of total health expenditure in different countries) is presented although apart from the USA few countries have assessed the economic consequences. There is insufficient evidence of effectiveness of strategies to prevent obesity in adults and there is a need to develop comprehensive and multi-component of strategies. Intersectional policy and environmental initiatives in addition to behavioural change approaches in national and international scale should be considered. This thesis showed that obesity is an important public health, medical, social and economic problem and should be considered from many prospectives by individuals, communities, policy makers, researchers, health providers and health managers.