Haloperoxidases (EC group 1.11.1) are enzymes that catalyze the oxidation of a halide (i.e., chloride, bromide, or iodide) by dihydrogen peroxide (generally known as hydrogen peroxide), which results in the halogenation of organic substrates, the production of the corresponding hypohalous acid, or the production of dioxygen by the subsequent reduction of the oxidized halogen species by a second equivalent of dihydrogen peroxide. The nomenclature for the haloperoxidases has historically been based on the most electronegative halide of which the enzyme can catalyze the oxidation by dihydrogen peroxide. Thus chloroperoxidase can catalyze the oxidation of chloride, bromide, and iodide by dihydrogen peroxide; bromoperoxidase can catalyze the oxidation of bromide and iodide by dihydrogen peroxide; and iodoperoxidase can only catalyze the oxidation of iodide by dihydrogen peroxide.