Advances in technology have allowed for the expansion of the field of epigenetics, providing a deeper understanding of geneenvironment interactions. Investigations into the neurobiological basis of substance abuse have benefitted from these advances, with findings suggesting that epigenetic mechanisms underlie drug-induced modifications of brain morphology, synaptic plasticity, and behavior. Epigenetic marks likely mediate the long-lasting and potentially transgenerational alterations of neuronal chromatin and subsequent gene expression that may lead to persistent relapse vulnerability and/or offspring vulnerability to addiction. Understanding the epigenetic mechanisms as well as potential sensitive windows for these alterations may provide novel insight into how epigenetics factor into the individual vulnerability and unique time periods for added vulnerability to illicit drug exposure. In the current review, we outline recent literature that provides evidence for early epigenetic changes in several addiction models. We begin the review with an overview of epigenetics as they relate to drug use and abuse, and next focus on findings in the context of prenatal, childhood, and adolescent stages with additional references to adult models of addiction. Further, we also focus on studies that discuss the transgenerational inheritance of epigenetic changes, and how they may affect the individual across development. Lastly, the work presented here and potential future studies focus on demonstrating early disruptions in epigenetic marks following acute or repeated drug exposure that may be of relevance in the broader goal of identifying risk factors and novel targets for addiction treatment.