Progesterone is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy (supports gestation) and embryogenesis of humans and other species. Progesterone belongs to a class of hormones called progestagens, and is the major naturally occurring human progestagen.

It is important that Progesterone not be confused with progestins, which are synthetically produced progestagens.

Other terms for progesterone include lutren, lutein, flavolutan, corporin, and luteal hormone.