An Alive & Thrive (A&T) study in Viet Nam examined determinants of the gap between breastfeeding awareness and practices. Although awareness among mothers about optimal breastfeeding practices was good, the prevalence of early initiation of breastfeeding, exclusive breastfeeding (EBF), and continued breastfeeding at 2 years in Viet Nam was low. Findings showed that the gap between awareness and practice for early initiation of breastfeeding was smaller when mothers received breastfeeding support by a health worker but was larger with medical complications, breastfeeding difficulty, and intention of feeding infant formula at birth. The awareness-practice gap for EBF was smaller among women who believed that EBF was the social norm. Breastfeeding awareness will not necessarily be translated into practice without strengthening breastfeeding support, minimizing barriers, and addressing social norms.