Social norms marketing has become a widely used technique for promoting pro-social behaviors, however, little is known about the cognitive changes produced by these interventions. The purpose of the present study was to investigate the extent and durability of changes in normative beliefs following a one-shot social norms communication. Participants were surveyed immediately following the intervention, one week later, and one month later. Results showed that (1) normative beliefs spilled over to behaviors and referents not specified in the original message; (2) communication and self-knowledge both contributed to participants’ normative belief estimates; and (3) the change in normative beliefs over the one-month period was consistent with Miller and Prentice’s (1996) theory of normative belief construction. Possible explanations for the spillover effect are discussed.