Delineating the mechanisms of long-term effects is an important and highly challenging objective in toxicology. For example, it is critical to delineate the impacts of exposure to stressors during the highly vulnerable early life developmental period. It has been shown that such exposures lead to toxic outcomes later in life, but the mechanisms underlying such effects remain elusive. One possible mechanism is through epigenetic regulations since their properties can account for delayed effects. In this chapter we will provide several examples showing the relevance of epigenetic regulations: the Dutch hunger and its long lasting effects on in utero exposed individuals, the epigenetic effects of smoking, of endocrine disruptors such as obesogens. We will also describe animal models used to explore epigenetic effects. Evidence for transgenerational effects will be presented as well as the possible contribution of epigenetic mechanisms. Finally we critically discuss different mechanisms involving epigenetic regulations and their roles in biological communications.