The sequencing of the human genome was a milestone for biology and medicine – but not all is written in our genes. Scientists are now presenting a second chapter of the book of life: Over the last five years, a worldwide consortium of scientists has established epigenetic maps of 2,100 cell types. Within this coordinated effort, CeMM contributed detailed DNA methylation maps of the developing blood, opening up new perspectives for the understanding and treatment of leukemia and immune diseases.