Physiological roles of Cl−, a major anion in the body, are not well known compared with those of cations. This review article introduces: (1) roles of Cl− in bodily and cellular functions; (2) the range of cytosolic Cl− concentration ([Cl−]c); (3) whether [Cl−]c could change with cell volume change under an isosmotic condition; (4) whether [Cl−]c could change under conditions where multiple Cl− transporters and channels contribute to Cl− influx and efflux in an isosmotic state; (5) whether the change in [Cl−]c could be large enough to act as signals; (6) effects of Cl− on cytoskeletal tubulin polymerization through inhibition of GTPase activity and tubulin polymerization-dependent biological activity; (7) roles of cytosolic Cl− in cell proliferation; (8) Cl−-regulatory mechanisms of ciliary motility; (9) roles of Cl− in sweet/umami taste receptors; (10) Cl−-regulatory mechanisms of with-no-lysine kinase (WNK); (11) roles of Cl− in regulation of epithelial Na+ transport; (12) relationship between roles of Cl− and H+ in body functions.