The term epigenetics describes regulatory and information storing mechanisms of specific genes that do not involve any change of their DNA sequence. Epigenetics is closely related to the extensively folded state, in which the genome is packaged, known as chromatin. New genomic tools nowadays allow the genome-wide assessment of, for example, chromatin states and DNA modifications, and led to the discovery of unexpected new epigenetic principles, such as epigenomic memory. This was the start of the field of epigenomics, the relation of which to human health and disease is discussed in this textbook.