Glutathione (GSH, gamma-L-glutamyl-L-cysteinylglycine) is a tripeptide synthesised in the cytosol of animal cells and is the most abundant low-molecular-weight thiol; the GSH/glutathione disulfide pair is the major redox couple in animal cells. Because it is an endogenous metabolite, the literature is large and largely biochemical. Reviews cover its synthesis and regulation, its role in antioxidant defence and conjugation of electrophiles, methods for measuring cellular GSH status, and more recent work on redox signalling.