An increasing number of publications have evaluated various breastfeeding peer counseling models. This article describes a systematic review of (a) the randomized trials assessing the effectiveness of breastfeeding peer counseling in improving rates of breastfeeding initiation, duration, exclusivity, and maternal and child health outcomes and (b) scientific literature describing the scale-up of breastfeeding peer counseling programs. Twenty-six peer-reviewed publications were included in this review. The overwhelming majority of evidence from randomized controlled trials evaluating breastfeeding peer counseling indicates that peer counselors effectively improve rates of breastfeeding initiation, duration, and exclusivity. Peer counseling interventions were also shown to significantly decrease the incidence of infant diarrhea and significantly increase the duration of lactational amenorrhea. Breastfeeding peer counseling initiatives are effective and can be scaled up in both developed and developing countries as part of well-coordinated national breastfeeding promotion or maternal-child health programs.