The Encyclopedia of DNA Elements (ENCODE) project has systematically mapped regions of transcription, transcription-factor association, chromatin structure and histone modification. In this overview, the Consortium guides the readers through the project itself, the data and their integrated analyses. Eighty per cent of the human genome now has at least one biochemical function assigned to it. In addition to expanding our understanding of how gene expression is regulated on a genome-wide scale, the newly identified functional elements should help researchers to interpret the results of genome-wide associated studies because many correspond to sites associated with human disease.