The term progesterone should only be used for the natural hormone produced by the ovaries or included in a registered drug. The modern history of progesterone begins with the first book-length description of the female reproductive system including the corpus luteum and later with the Nobel Prize winner, Adolf Butenandt who took a crucial step when he succeeded in converting pregnanediol into a chemically pure form of progesterone, the corpus luteum hormone. The deficient production of progesterone was shown first to be the cause of the luteal-phase deficiency responsible for infertility and early pregnancy loss due to inadequate secretory transformation of the endometrium. Later, progesterone was confirmed to be the best and safest method of providing luteal-phase support in assisted reproductive technology. Progesterone provides adequate endometrial protection and is suggested to be the optimal progestagen in menopausal hormone therapy in terms of cardiovascular effects, venous thromboembolism, probably stroke and even breast cancer risk. Neuroprotective effects of progesterone have also been demonstrated in several of experimental models including cerebral ischemic stroke and Alzheimer’s disease. Vaginal progesterone was shown to decrease the risk of preterm birth in women with a mid-trimester sonographic short cervix and to improve perinatal outcomes in singleton and twin gestations.