This book covers many facets of plant selenium (Se) accumulation: molecular genetics, biochemistry, physiology, and ecological and evolutionary aspects. Broader impacts and applications of plant Se accumulation also receive attention. Plant Se accumulation is very relevant for environmental and human health. Selenium is both essential at low levels and toxic at high levels, and both Se deficiency and toxicity are problems worldwide. Selenium can positively affect crop productivity and nutritional value. Plants may also be used to clean up excess environmental Se. Selenium in plants has profound ecological impact, and likely contributes to Se movement in ecosystems and global Se cycling.