Non-shivering thermogenesis in brown adipose tissue (BAT) is a crucial physiological adaptation in many newborn mammals (including humans), which assists in the maintenance of core body temperature before insulatory white fat stores are deposited. Whilst the amount of BAT in adipose depots decreases with advancing age, it can still be recruited in adults in response to physiological challenges including cold (cold-induced thermogenesis) and excess caloric intake (diet-induced thermogenesis). The capacity of individuals for diet-induced thermogenesis has an important impact on their ability to resist weight gain in response to increased energy intake – and therefore their risk of overweight and obesity. In this presentation, I will discuss the evidence that an individual’s capacity for BAT thermogenesis can have its origins in the nutrient environment experienced before birth and/or in early infancy – and that being exposed to an inappropriately high or inappropriately low nutrient supply during this perinatal period can result in a life-long reduction in an individual’s capacity for diet-induced thermogenesis, and a consequent increase in their susceptibility to diet-induced obesity. This is of particular importance given the recent studies which have shown that BAT is present in significant amounts in adult humans, and not just in rodents and hibernating mammals as was previously thought, and that the programming of BAT thermogenic  function is therefore likely to play a role in the early life origins of human obesity.