Plants possess a sophisticated array of systems with which to sense and respond to their internal and external environment. Biological changes triggered by such systems represent examples of phenotypic plasticity. One aspect of phenotypic plasticity that has recently emerged is transgenerational priming of plant defence responses – the persistence of induced resistance responses across generations. There has been a recent surge in interest in epigenetic mechanisms as a basis for phenotypic plasticity, including the ability for such epigenetic changes to be inherited across generations. In this review, we focus on the evidence that attack by pests and disease can stimulate plant defence responses that increase levels of resistance not only in attacked plants, but in their offspring, and discuss mechanisms by which environmental stress signals can be inherited. Finally, we consider the implications of transgenerational defence responses for plants in natural and agricultural systems.