Breastfeeding is important for women and children’s health, but less than half of infants worldwide begin life with optimal breastfeeding. A growing literature shows consistently large economic costs of not breastfeeding, with global studies showing economic losses of around US$300 billion globally. However, existing studies are highly diverse in approaches, methods, data sources, and country results.Building on a landmark 2012 UNICEF UK review focused on high-income countries, we conducted a scoping review to map and characterize the expanding literature and identify future research directions in this research area. We included studies (n=36) in diverse country settings and outcomes for women and children. We used PubMed, Web of Science, EMBASE, MEDLINE, ProQuest, and manual searches of cost of not breastfeeding studies published between 1996 and 2023. Articles were excluded if they were macroeconomic evaluations, did not assign monetary values, or only evaluated breastfeeding or formula feeding costs and not outcomes, or were cost of programs studies.We found considerable diversity in disciplinary approaches and differences in methodologies. Though there were different cost measurement perspectives (societal, institutional/payer, and individual), all but two excluded the costs of unpaid care. Studies typically measured costs of medical treatment, with more recent studies using dynamic simulation models.The largest economic costs were derived from lifetime estimates of human capital losses, namely cost of premature death and loss of IQ points. Medical and death costs varied widely depending on method of calculation, but total costs consistently exceeded $US 100 billion annually for the United States, and around $US300 billion in global studies.Our findings suggest that greater interdisciplinary collaboration is needed particularly to better define infant feeding exposures, and advance comprehensive measurement of costs and outcomes across lifetimes, in order to prioritise breastfeeding as a public health strategy of economic importance.