Whilst the primary DNA sequence sets the limits of potential gene expression, the pattern of gene expression in a given cell under particular circumstances is determined by several factors including the epigenetic marking of the genome. These marks include DNA methylation and post-translational modification of the histones around which DNA is wrapped when packaged in the nucleus. Importantly, these marks are malleable in response to environmental exposures and contribute to phenotypic plasticity in the context of a fixed genotype. There is now proof of principle that maternal diet can have a profound impact on the epigenome and so determine gene expression patterns and health throughout the life-course. Studies of altered epigenetic marking will be of profound importance for mechanistic understanding of the role of nutrition in health but especially for studies of the developmental origins of health.