There are a growing number of publications evaluating various breastfeeding peer counseling (PC) models. We have systematically reviewed a) the randomized trials assessing the effectiveness of breastfeeding PC in improving rates of breastfeeding initiation, duration, exclusivity and maternal and child health outcomes; and b) scientific literature describing the scale-up of breastfeeding PC programs. Twenty-six peer-reviewed publications were included in this review. The overwhelming majority of evidence from randomized, controlled trials evaluating breastfeeding PC indicates that peer counselors effectively improve rates of breastfeeding initiation, duration and exclusivity. PC interventions were also shown to significantly decrease the incidence of infant diarrhea and significantly increase the duration of lactational amenorrhea. We conclude that breastfeeding PC 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.