Chloroformic acid is a chemical compound with the formula ClCO₂H. It is the single acyl-halide derivative of carbonic acid (phosgene is the double acyl-halide derivative). Chloroformic acid is also structurally related to formic acid, in a way that the non-acidic hydrogen of formic acid is replaced by chlorine. Despite the similar name, it is very different from chloroform. It is described as unstable, decomposing into carbon dioxide and hydrogen chloride.

Chloroformic acid itself is too unstable to be handled for chemical reactions. However, many esters of this carboxylic acid are stable and these chloroformates are important reagents in organic chemistry. They are used to prepare mixed carboxylic acid anhydrides used in peptide synthesis. Important chloroformate esters include 4-nitrophenyl chloroformate, fluorenylmethyloxycarbonylchloride, benzyl chloroformate and ethyl chloroformate.