Epigenetics, broadly defined as the regulation of gene expression without alteration of the genome, has become a field of tremendous interest in neuroscience, neurology, and psychiatry. This research has rapidly changed the way researchers think about brain function. Exciting epigenetic discoveries have been found in addiction, early life stress, neurodegeneration, post-traumatic stress disorder, and depression. As researchers more precisely define the epigenetic landscape that regulates disease progression in each of these cases, therapeutics can be designed to specifically target the molecules that mediate these epigenetic processes. Further, epigenetics may lead, to the identification of novel biomarkers for diagnosis and for the monitoring of treatment. Epigenetic profiling is likely to become a routine tool for the diagnosis of neurological and psychiatric disorders in the near future.