The incidence of obesity is on the increase in affluent societies, and the phenomenon commands increasing attention from health professionals, legislators and the media. This unit looks at the science behind obesity, examining the dietary, physiological and genetic aspects of the topic. This study unit is just one of many that can be found on LearningSpace, part of OpenLearn, a collection of open educational resources from The Open University. Published in ePub 2.0.1 format, some feature such as audio, video and linked PDF are not supported by all ePub readers.