The human genome has been decoded, but it contains far fewer pieces of information than expected. A second layer beyond the genes has come into focus in the scientific community: epigenetics. In addition to the DNA sequence, but closely connected to it, there exists a second, even a third and fourth layer of information. These epigenetic programs can turn entire chromosomes on and off. They are what elicit the complex and infinitely diverse music of life from the keyboard of genes. In all of this, they serve as a hinge between the environment and the genome, acting as a kind of missing link that brings the old debate about the significance of genes and environment into a new phase. The findings of epigenetics gain particular urgency due to their foreseeable consequences for medicine and evolutionary biology, addressing the major questions of life sciences.