Although Vietnam has a strong regulatory environment for the protection, promotion, and support of breastfeeding, there are implementation, monitoring, and enforcement gaps. This study examined the enactment and implementation of the Code of Marketing of Breast-Milk Substitutes (the Code) in Vietnam with a focus on marketing practices by the baby food industry and perceptions of caregivers, health workers, and policy makers. A survey of 268 pregnant women and 726 mothers of infants aged 0–11 months and in-depth interviews with a subset of interviewed women (n = 39), policy makers, media executives, and health workers (n = 31) showed that although facilities have rules against BMS promotion, these rules are violated and, in particular, that BMS companies representatives obtain mothers' contact information at health facilities and then market their products to them In the 30 days preceding the survey, one-fifth of pregnant women were exposed to promotions of commercial milk formula for pregnant women and 7.1% to promotions of BMS. Among mothers of infants, 7.3% and 10.7% of respondents with infants aged 0–5 and 6–11 months, respectively, were exposed to some form of BMS promotion in the past 30 days. Stronger enforcement of national policies to regulate the presence of BMS industry representatives in health facilities—both public and private—and the promotion of BMS products on digital platforms are needed.