Cis-acting binding sites for transcription activators cannot explain the patterned expression of genes during development, nor a large range of phenomena that result from gene transplacement. Heritable states of transcriptional regression or activation sequences are influenced not only by the chromosomal context of the promoter but also by modifications of histones and DNA, and long-range interactions between distant chromosomal elements. The molecular dissection of these epigenetic phenomena has become an exciting topic of research, revealing highly conserved mechanisms at work in chromatin-mediated gene control.