The distribution of obesity in developed countries follows a social gradient. In developing countries, a similar pattern is emerging as national per capita income rises. The epidemiological evidence runs counter to the popular opinion that being overweight and obesity are matters solely of individual lifestyle choices or genetics. Both are important, but in themselves do not explain the social gradient in being overweight and obesity, to understand which, one needs to look at wider social influences. Evidence from studies including the Whitehall Study of British civil servants indicates that psychosocial factors, including stress, as well as material factors associated with position in the social hierarchy, contribute to the distribution of being overweight and obesity, particularly central adiposity, in the population.