17β-Hydroxysteroid dehydrogenases (EC 1.1.1.51, beta-hydroxy steroid dehydrogenase, 17-ketoreductase, 17beta-hydroxy steroid dehydrogenase, 3beta-hydroxysteroid dehydrogenase, 3beta-hydroxy steroid dehydrogenase, 17β-HSD, 17-ketosteroid oxidoreductases, HSD17B, 17-ketosteroid reductases, 17-KSR), are a group of alcohol oxidoreductases which catalyse the dehydrogenation of 17-hydroxysteroids in steroidogenesis.