Varied environmental compartments such as soil and water potentially contaminated with different metals/metalloids can impact the health of both plants and animals/ humans. Trace amounts of Cu, Mn, Mo, Ni and Zn are beneficial for higher plants, whereas, Cr, Cu, Co, Mn, Mo, Se, V and Zn are known as the micronutrient metal/metalloids for animals/humans. However, elevated levels of the metals/metalloids can cause severe toxic consequences in both plants and animals/humans. Common in plants and animals/humans, phytochelatins PCs , the principal non-protein, S-rich, thiolate peptides, protect through different mechanisms cellular functions and metal/metalloid homeostasis by performing their chelation and/or detoxification. With the major aim of broadening the current knowledge on the subject, this chapter a overviews PCs role and modulation separately in metal/metalloid-exposed plants and animals/humans b discusses major methods for determination of PCs and bioassays for enzymes involved in PC synthesis c evaluates the connection of PCs with bionanoparticles and finally d highlights so far unexplored aspects in the present context.