Context: Lactation causes a delay in ovulation in the postpartum period, and therefore a delay in the resumption of menses. However, return to fertility is variable in the postpartum period and is contingent upon numerous factors. The postpartum period is therefore a critical time to initiate effective contraception in order to support the numerous beneficial health outcomes of optimal pregnancy spacing. Breastfeeding women have an unmet need for highly effective birth control methods that do not interfere with lactation and that are safe for their infants. The progesterone-releasing vaginal ring (PVR) releases a natural progesterone that suppresses ovulation and is specifically designed for breastfeeding women in the first postpartum year. Objective: To review the published peer-reviewed literature regarding the safety and effectiveness of the PVR used for contraception among lactating women, as well as the safety for their infants. Results of this review informed the decisions of the Guideline Development Group to include recommendations on contraceptive eligibility for the PVR within the World Health Organization Medical Eligibility Criteria for Contraceptive Use, 5th Edition. Methods: We searched the PubMed, Popline, and LILACS bibliographic databases for articles published in any language from database inception through October 1, 2014. We reviewed the literature for evidence regarding the safety of the PVR among breastfeeding women using the method, as well as for their infants. The US Preventive Services Task Force system was applied to assess the quality of the evidence. Results: Seven articles met our criteria for inclusion in this review. All studies were of a prospective cohort design. All studies consistently showed that use of the PVR among breastfeeding women compares favorably to other methods of contraception with regard to effectiveness, does not compromise a woman's breastfeeding performance, and does not adversely affect infant growth during the first year postpartum. Conclusion: The PVR is a safe and highly effective method of contraception for use among breastfeeding women. It should be offered to women who plan to breastfeed in the context of postpartum contraceptive counseling. (C) 2016 Published by Elsevier Inc.