Chlorosulfuric acid (IUPAC name: sulfurochloridic acid) is the inorganic compound with the formula HSOCl. It is also known as chlorosulfonic acid, being the sulfonic acid of chlorine. It is a distillable, colorless liquid which is hygroscopic and a powerful lachrymator. Commercial samples usually are pale brown or straw colored.
Salts and esters of chlorosulfuric acid are known as chlorosulfates.