In the developed world the number of obese people is increasing rapidly. In many countries more than one third of the adult population is overweight or obese. Not surprisingly, the subject of weight control is of enormous interest, both from a scientific perspective in the medical profession and practically among the general population. Although there has been much research into the mechanisms of controlling body weight, in the past there has been little success in stemming or reversing this trend. However, the advent of techniques for measuring energy expenditure together with approaches to the assessment of the various influences on eating behaviour, has led to progress. We now have a clearer understanding of the aetiology of obesity and consequently better approaches to treatment and prevention of this condition are being devised. This text outlines the current state of research in the area and provides pointers to the future.