Mifepristone is a steroid compound derived from the estrane progestins. This compound strongly binds to the progesterone and glucocorticoid receptors, and to a lesser extent to the androgen receptor. As a result, this drug has a potent antiprogesterone, antiglucocorticoid and weak antiandrogen actions. Its main use as an abortifacient is due to the block of progesterone action which increases the uterine contractility, sensitises the myometrium to prostaglandins, and elicits cervical maturing. This book discusses mifepristone on a vascular level, and provides the advantages and disadvantages of antiglucocorticoid and antiprogesterone activity of mifepristone. It also discusses the beneficial effects that this anitprogestin has in breast cancer.