Aim: To assess the current scientific evidence about the relationship between breastfeeding and the development of infant's socio-emotional competencies. Materials and Methods: A systematic review of literature was conducted through PubMed, LILACS ( Literatura Latinoamericana y del Caribe en Ciencias de la Salud ), and PsycINFO of population-based cohorts. Records were screened, data extracted, and a quality assessment performed by two authors independently. Results: Thirteen studies were included in the review with six finding a statistically significant association between breastfeeding and the development of socio-emotional competencies such as problem solving, agreeableness, and optimism. In five studies, no statistically significant association was found, and in three, a negative association existed. Regarding quality assessment, four studies had a strong global rating, four had a moderate rating, and five had a weak global rating. Conclusion: Almost half (6/13) of the studies found a positive association between breastfeeding and the development of social-emotional competencies in infants; however, a great heterogeneity was present in the quality of the included studies. There is a need for further and higher quality research into this field of study.