17 beta -Hydroxysteroid dehydrogenases (17 beta -HSD) are pivotal in controlling the biological potency of steroid hormones by catalyzing oxidation or reduction at position 17. Several 17 beta -HSDs may as well metabolize further substrates including alcohols, bile acids. fatty acids and retinols. This review summarizes recent progress in the field of 17 beta -HSD research provides an update of nomenclature.