Abstract: Plastic waste pollution remains a major problem across the developing world. In Vietnam, the situation is particularly serious as many plastic consumption behaviours remain under-analysed and pertinent policies have produced limited impact. Accordingly, this paper examines the patterns and predictors of consumer plastic bag use when shopping in Da Nang, Vietnam. It does so by drawing on an original household survey and key informant interviews. Moreover, it applies the latest behavioural theory research and machine learning techniques. Subsequently, this paper observes Vietnamese consumers’ plastic bag use is prevalent and often entrenched as a habit. Additionally, two socio-demographic and seven socio-psychological predictors are significant to the frequency of using plastic bags. These results, then, inform Vietnam’s plastic consumption policies and, more broadly, emphasise the (1) heterogeneity of influences on consumer behaviour; (2) contingency of many widely-accepted behavioural predictors; and (3) shortcomings of purely regulatory solutions.