Two twin sisters, one with and one without asthma. Two genetically identical mice, one black and lean, the other yellow and obese. Two human cells, one from the brain and the other from the skin: they look and act different, but they have the same DNA sequence. All of this is the work of epigenetics. Much emphasis has been placed on DNA and genes as repositories of the code designed to transmit information and dictate biological programs. However, developmental trajectories and responses to environmental cues are – and need to be – highly plastic. This plasticity is made possible by epigenetic mechanisms that enhance or silence gene expression at the right time in the right environmental context but do not change the DNA sequence. Thus the code inscribed in our DNA is necessary but not sufficient to recapitulate our biological identity and determine our biological destiny. This lecture will explore how understanding epigenetics will advance our understanding of human biology and disease.