The sum of all the chemical modifications to DNA or chromatin that influence the activity of genes but do not affect the sequence of bases—i.e. changes that are literally ‘above the genome’. These epigenetic tags play a key role in determining which genes are active or inactive in particular tissues, and they can be inherited by offspring. Epigenomics is the study of the epigenome, how it is influenced by environmental and cellular factors, and the role it plays in controlling gene expression and hence cellular function in health and disease. See also chromatin remodelling.