The relationships between dietary and environmental factors and obesity are reviewed. Findings from selected population studies of diet and body weight are presented. In general, the results from population studies of diet and obesity have been inconsistent and marked with methodological weaknesses, especially the use of cross-sectional study design. Apart from the diet, several social and economic factors appear to be important correlates of obesity in the population. However, most studies have focused on the socioeconomic status as a broad, composite measure. The relationships between income, education, occupation, place of residence, and obesity are reviewed here, with emphasis on the developing countries. In many developing countries, the changing dietary pattern, along with rising life expectancy and changing socioeconomic environment, has contributed to the increasing problems of obesity and other diet-related chronic diseases that will have an enormous impact on the health and health care resource of these countries in the near future.