Although selenium (Se) is an essential element for many prokaryotes, archaebacteria and eukaryotes, it is not required by either fungi or higher plants (White 2016). Nevertheless, Se is taken up, translocated and metabolised by higher plants because of its chemical similarity to sulphur (S). Tissue Se concentrations in an individual plant are largely determined by the Se phytoavailability in the substrate in which the plant is growing and the plant’s capacity for S uptake, translocation, and assimilation (White 2016, 2018a, b). Since excessive Se accumulation in plant tissues can be toxic, the maximum tissue Se concentration in a living plant is determined by its ability to tolerate Se physiologically (White 2016). Most plants that grow on non-seleniferous soils cannot tolerate tissue Se concentrations greater than 10 to 100 mg Se/kg dry matter (DM). However, some plant species have evolved greater Se tolerance and can accumulate more than 100 mg Se/kg DM in their tissues. Plant species that can colonise both non-seleniferous and seleniferous soils are termed “Se indicator” plants, whereas those that only grow on seleniferous soils are termed “Se accumulator” plants. Some Se accumulator plants can have tissue Se concentrations of 1000 to 15,000 mg Se/kg DM when growing their native environment and are termed “Se hyperaccumulator” plants. However, fewer than 60 species have been reported that hyperaccumulate Se (White 2016). There is considerable genetic variation within all plant species in both Se accumulation and tissue Se tolerance. It is thought that this genetic variation (1) led to the evolution of plant species that colonised seleniferous soils (White 2016, 2018a) and (2) might be used in agriculture to develop crop genotypes with greater Se concentrations in their edible portions to improve the nutrition of humans and their livestock (White & Broadley 2009, White 2016). This article first reviews the genetic variation in Se accumulation between plant species and then the genetic variation in Se accumulation that occurs within plant species.