There is convincing evidence that tumorigenesis results from mutations in DNA that lead to critical changes in cell metabolism and are inherited as a cell divides itself. However, the process of tumorigenesis can also be strongly influenced by epigenetic factors. Epigenetic inheritance is defined as inheritance that does not follow normal Mendelian patterns and may involve nuclear mcb.200300157s in addition to DNA. We now have significant information about the molecular mechanisms that influence epigenetic inheritance. Most of these mechanisms include direct modifications of either DNA itself or the collection of proteins, called histones, which intimately associate with DNA. Unlike DNA mutations, epigenetic events are often reversible, making them exciting new targets for therapy. This understanding is leading to the development of specific drugs that target epigenetic events and thus may complement existing cancer treatments.