Epigenetic processes play a central role in regulating the tissue-specific expression of genes. Alterations in these processes can therefore lead to profound changes in phenotype and have been implicated in the pathogenesis of many human diseases. However, there is now evidence that the epigenome is susceptible to a range of environmental cues such as variations in diet, maternal behaviour or stress during specific developmental periods. The environmental sensitivity of the epigenome has been suggested to reflect an adaptive mechanism, by which the organism can adjust its metabolism and homeostatic systems to suit the environment, in order to aid survival or reproductive success in later life. Inappropriate adaptation has been linked to the development of a range of chronic diseases in later life and has been suggested to account for at least some of the rapid increases in the rates of obesity, type II diabetes and cardiovascular disease recently observed in both developed and developing countries. This chapter will therefore focus on how nutritional cues in the environment can alter the epigenome, producing different phenotypes and altered disease susceptibilities from a single genotype.