variation of sequence elements present in the genome. An immediate question that surfaced was how one single genome can give rise to all the different cell types of the human body, and how all these different cell types know how and when to interpret these genomic elements. Since then, it has become widely appreciated that this regulation of DNA elements is closely connected to how the DNA is packaged within the nucleus of each individual cell. This packaging is orchestrated via chromatin, the complex of DNA, RNA and proteins that provides functionality to the genome. Chromatin is, in contrast to DNA, highly dynamic, and this plasticity is achieved through placing chemical tags on cytosines at the DNA level and on histones at the nucleosome level providing an index or blueprint on top of the genomic information in different cellular environments (Figure 1). 2, 3 The field of epigenetics aims to define the combination of chemical tags that index the genome, how these marks are recognized and how this translates into specific gene regulation and interpretation of the functionality of DNA elements. Initially, epigenetic studies focused on single loci or genomic regions of several kilobases, but technological advances in recent years have for the first time allowed the establishment of genome wide epigenomic maps of individual cell types. To face the challenge of the plasticity and the shear number and diversity of epigenetic marks, worldwide consortia have been founded which aim to establish epigenomic maps of different kinds for a variety of species. Specific for human, these efforts are coordinated by the International Human Epigenome Consortium (IHEC; http://www. ihec-epigenomes. org/) that aims to deliver 1,000 reference epigenomes for human cell types. Within IHEC, quality standards are set for every aspect of epigenomic mapping, from experimental setup and metadata collection to data storage and primary analysis. Moreover, it provides communication platforms that allow data sharing and minimizes redundancy between different individual research projects. Currently, seven epigenomic projects have been initiated and more are expected to join IHEC in the coming years.