Emergency contraception is used after unprotected intercourse or a contraceptive accident to prevent unwanted pregnancy. It is thought to work by stopping or delaying ovulation or preventing implantation if fertilization has already taken place. Hormonal methods, mifepristone, and intrauterine device insertion are among the methods used worldwide. Combination estrogen-progestin birth control pills are the most commonly used form of emergency contraception in the United States. According to the Yuzpe method, combination pills are taken within 72 hours after intercourse, followed by a second identical dose 12 hours later. With this method, the number of unintended pregnancies is reduced by about 75%. Nausea and vomiting are the most troublesome adverse effects, but these can be controlled with antiemetic medication taken prior to the first dose. The Food and Drug Administration, Washington, DC, has approved an emergency contraception kit consisting of 4 combination pills, a urine pregnancy test, and a patient information book. Most recently, the Food and Drug Administration has approved a progestin-only formulation, which has fewer adverse effects and equal or improved efficacy compared with the combination formula. An intrauterine device can be inserted up to 5 days after unprotected intercourse and is a cost-effective option if it is used as ongoing contraceptive protection. The most readily available form of emergency contraception consists of 2 doses of estrogen-progestin combination birth control pills or 2 levonorgestrel pills taken 12 hours apart. Emergency contraception should not be considered as an alternative to ongoing contraceptive methods, but can prevent unwanted pregnancy.