The Holocaust left its visible and invisible marks not only on the survivors, but also on their children. Instead of numbers tattooed on their forearms, however, they may have been marked epigenetically with a chemical coating upon their chromosomes, which would represent a kind of biological memory of what the parents experienced. as a result, some suffer from a general vulnerability to stress while others are more resilient. Previous research assumed that such transmission was caused by environmental factors, such as the parents' childrearing behavior. New research, however, indicates that these transgenerational effects may have been also (epi) genetically transmitted to their children. Integrating both hereditary and environmental factors, epigenetics adds a new and more comprehensive psychobiological dimension to the explanation of transgenerational transmission of trauma. Specifically, epigenetics may explain why latent transmission becomes manifest under stress. a general theoretical overview of epigenetics and its relevance to research on trauma transmission is presented.