Unspecific peroxygenases (UPOs) secreted by fungi represent an intriguing enzyme type that selectively transfers peroxide-borne oxygen with high efficiency to diverse substrates including unactivated hydrocarbons. They contain a cysteine-ligated heme and catalyze hydroxylation, epoxidation, dealkylation, deacylation as well as hetero atom, halide and one-electron oxidations. Substrate spectra of UPOs resemble both those of P450 monooxygenases and heme peroxidases.