Chromatin is a highly dynamic structure that undergoes a variety of chemical modifications. These modifications mediate alterations of the chromatin architecture, generate binding platforms that are recognized by other proteins, and are important elements of epigenetic gene regulation. An array of antagonizing histone modifying enzymes that catalyze the attachment and removal of a number of chemical groups has been described and their biologic role has been an intense area of research. With the recent discovery of the first histone demethylase, lysine-specific demethylase-1, a dynamic view of histone methylation was born. As a deeper understanding of their involvement in transcriptional regulation is gained, histone demethylases are becoming increasingly interesting targets for drug development.