The benefits of breastfeeding for both the infant and the mother are undisputed. Longer intervals between births decrease fetal/infant and maternal complications. Lactation is an effective contraceptive for the first 6 months postpartum only if women breastfeed exclusively and at regular intervals, including nighttime. Because a high percentage of women in the United States supplement breastfeeding, it is important for these women to choose a method of contraception to prevent unintended pregnancies. Both the method of contraception and the timing of the initiation of contraceptives are important decisions that a clinician must help the breastfeeding woman make. Ideally, the chosen method of contraception should not interfere with lactation. This article reviews the research on the effect of contraceptives, including hormonal contraceptives, on lactation.