The history of current knowledge of the synthesis and action of ovarian hormones is presented in this review of physiological and phamacological actions of endogenous and exogenous estrogens and progestins. The formation of estrogens is regulated by follicle stimulating hormone. Estrogens are ultimately formed from either androstenedione or teststerone as immediate precursors and the reaction of central importance is the aromitization of ring A. Of the main 3 estrogens of human beings estradiol 17 beta is the most potent and the major secretory product of the ovary; it is readily oxidized to estrone which in turn can be hydrated to estriol. Estrogens are responsible for puberty changes in girls conditioning feminine behavior and are responsible for many features of the normal menstrual cycle. Effects of estrogen on pituitary action are discussed as are the metabolic action of the sex hormone. In a few mammalian species estrogen administration is associated with tumor development. Estrogen mechanism of action assays and available preparations are outlined and its side effects and therapeutic uses are discussed. All of the above-mentioned topics (physiological and pharmacological actions; synthesis and secretion; mechanism of action; absorption fate and excretion; assays; preparations; and therapeutic uses and concomittent side effects) are covered for both antiestrogenic compounds (clomiphene) and progestational ones also.