This chapter describes clinical usage guidelines of progestins. The uses of progestins can be divided as diagnostic and therapeutic. Diagnostic use include progesterone challenge test (PCT). Progesterone challenge test (PCT) is used in patients with amenorrhea, whether primary amenorrhea, secondary amenorrhea, lactational amenorrhea or amenorrhea in perimenopausal period. Therapeutic uses include contraceptives, combined oral contraceptive pills, vaginal estrogen-progestin contraception, transdermal estrogen-progestin contraception, progestogen-only contraceptives, progestogen-only pill (POP), emergency contraceptive pill (ECP), ideal candidates for contraceptive implants, hormone replacement therapy, luteal phase defect (LPD), and premenstrual syndrome. Progestogens are used as contraceptives, either alone or in conjunction with estrogens. Progestogens act as contraceptives by various mechanisms.