Vernalisation is the response to a period of prolonged cold required by many plants to switch from vegetative to reproductive growth. Variation in the requirement for, and the response to, a period of weeks or months of cold underpins life history variation in both wild and crop species and ensures flowering occurs in the more optimal conditions in spring. In monocots and dicots three key players a gene activated by cold, a repressor, and an integrator have been identified within the vernalisation regulatory network. However, the relative importance of allelic variation at these genes to variation in vernalisation response differs between the two subdivisions of flowering plants. Genetic and molecular analysis of this variation has revealed a mechanism with core epigenetic components in the exemplar Angiosperm lineages Brassicaceae and Poaceae.