Genetics is broadly defined as the study of how genes control the characteristics of organisms. In this chapter, emphasis has been placed on differences in metabolic pathways, and their associated genes, that could account for variation in the ability of angiosperm species to tolerate large tissue selenium (Se) concentrations. The current view of the molecular biology of Se uptake and assimilation by plants is presented and differences between plant species likely to affect their ability to tolerate large tissue Se concentrations are identified. In particular, it is noted that plants that hyperaccumulate Se generally exhibit constitutive expression of genes encoding Se-transporters and enzymes involved in primary Se assimilation, biosynthesis of non-toxic Se metabolites and Se volatilisation. A plausible scheme for the evolution of differences in Se accumulation between angiosperm species is described. Since Se is an essential mineral element for animals, and the diets of many humans lack sufficient Se, the possibility of breeding crops with greater Se concentrations in their edible tissues is discussed. It is observed that, although Se concentrations in plants are largely determined by the phytoavailability of Se in the environment, there is significant intraspecific genetic variation in the Se concentrations of most edible crops that might be utilised to improve human diets. However, although molecular markers might be developed to known chromosomal quantitative trait loci (QTL) impacting Se concentration in edible tissues to assist breeding programmes, the actual genes underpinning this variation are largely unknown.