Estrogens are the key female hormones that induce the development of reproductive tissues and secondary sex characteristics. The effects of estrogens are mediated by binding to the estrogen receptors present in the cell cytosole which triggers the translocation of the receptor to the nucleus and transcription of DNA. Other beneficial effects include osteoclast inhibition, prevention of colon cancer, more favourable lipoprotein status, as well as protective cardiovascular effects. However, estrogens also promote the growth of breast cancer that expresses estrogen receptors. The therapeutic goal is the elimination of the estrogen effect on its receptors in the breast cancer tissue, which can be achieved through interference with estrogen biosynthesis or blockade of the estrogen binding to estrogen receptors. Drugs that interfere with estrogen biosynthesis are aromatase inhibitors, agonists and antagonists of gonadotropin-releasing hormone, and adrogens, whereas selective modulators of estrogen receptors and estrogen antagonists block the binding of estrogen. Inhibitors of cyclin-dependent kinases are also a valuable therapeutic option for estrogen-dependent breast cancer.