Plants in their natural environments are constantly subjected to biotic stress. In addition to possessing physical barriers and anti-nutritive toxins, plants can be primed to respond more efficiently against future attack via faster and stronger gene activation. Here we discuss recent findings showing that plants can pass signatures of attack to the next generation, thus rendering the progeny more resistant against insect and pathogen attack. A combination of phytohormone signaling, small RNA-mediated gene silencing and DNA methylation are involved in transgenerational induced resistance. Epiallelic variation against biotic threats should be under positive selection in populations of plants where the environment is predictable over time. Similarly, in very genetically homogenous populations, such as during range expansion, epigenome reorganization is a likely mechanism for faster plant adaptation to novel biotic attack. Further research is needed to understand the relative role of the genome vs. the epigenome for the evolution of increased plant resistance.