This review examines evidence relevant to the effect of hormonal contraception on breastfeeding; and compares global and US recommendations for contraceptive initiation and use. Breastfeeding and use of postpartum contraception have high public health priority, making research in this area critical for optimizing guidance.High-quality evidence remains limited with only a small number of well conducted randomized controlled trials of hormonal methods and breastfeeding/neonatal growth outcomes. More evidence supports early initiation of progestin-only methods. Evidence on early initiation of combination hormonal methods is sparse.The WHO Medical Eligibility Criteria (MEC) differs from that of the US MEC. Generally, the WHO MEC is more restrictive, reflecting the potential greater impact on maternal child health if there is a negative impact from hormonal contraception on breastfeeding. Only well conducted clinical trials will further elucidate such an impact.Video abstract: http://links.lww.com/COG/A15.