Hydroxylation of the benzoic ring by non-heme iron oxygenases having a Rieske-type cluster is the key step in the aerobic degradation of chloroaromatic compounds by bacteria. Rieske oxygenases (RO) catalyze the oxidative decarboxylation reaction unique to the enzymes of this family with the formation of corresponding phenolic compounds. This review discusses the general structure, function, and classification of ROs that catalyze the oxidation of chlorophenoxyacetic acids; genes encoding the ROs with their phylogenetic classes are also reviewed.