The chloride ion is formed when the element chlorine picks up one electron to form the negatively charged ion Cl. The salts of hydrochloric acid HCl are also called chlorides. An example is table salt, which is sodium chloride with the formula NaCl. In water, it dissociates into Na+ and Cl ions.

Chloride ions have important physiological roles. For instance, in the central nervous system the inhibitory action of glycine and some of the action of GABA relies on the entry of Cl into specific neurons.