Deciphering the information encoded in the human genome is key for the further understanding of human biology, physiology and evolution. With the draft sequence of the human genome completed, elucidation of the epigenetic information layer of the human genome becomes accessible. Epigenetic mechanisms are mediated by either chemical modifications of the DNA itself or by modifications of proteins that are closely associated with DNA. Defects of the epigenetic regulation involved in processes such as imprinting, X chromosome inactivation, transcriptional control of genes, as well as mutations affecting DNA methylation enzymes, contribute fundamentally to the etiology of many human diseases. Headed by the Human Epigenome Consortium, the Human Epigenome Project is a joint effort by an international collaboration that aims to identify, catalog and interpret genome-wide DNA methylation patterns of all human genes in all major tissues. Methylation variable positions are thought to reflect gene activity, tissue type and disease state, and are useful epigenetic markers revealing the dynamic state of the genome. Like single nucleotide polymorphisms, methylation variable positions will greatly advance our ability to elucidate and diagnose the molecular basis of human diseases.