The human costs of not breastfeeding are enormous: 600,000 children and 100,000 women die every year due to illnesses that could be prevented by breastfeeding. This advocacy brief presents the key findings of the Cost of not breastfeeding tool developed by researchers health economist Dr. Dylan Walters and Roger Mathisen and Dr. Linh TH Phan of Alive & Thrive, and outlines the actions donors and p;olicymakers can take to support breastfeeding. Brief also available in French.