Epigenetics refers to heritable changes that control how the genome is accessed in different cell-types and during development and differentiation. Even though each cell contains essentially the same genetic code, epigenetic mechanisms permit specialization of function between cells. The state of chromatin, the complex of histone proteins, RNA and DNA that efficiently package the genome, is largely regulated by specific modifications to histone proteins and DNA, and the recognition of these marks by other proteins and protein complexes. The enzymes that produce these modifications (the 'writers'), the proteins that recognize them (the 'readers'), and the enzymes that remove them (the 'erasers') are critical targets for manipulation in order to further understand the histone code and its role in biology and human disease.