This article draws on social dilemma theory and reference group theory to understand the individual boycott decision and tests the predictions stemming from this conceptualization in two experiments. Consistent with our predictions, consumers' likelihood of participating in both economic and social-issue boycotts is jointly determined by their perceptions of the boycott's likelihood of success, their susceptibility to normative social influences, and the costs they incur in boycotting. Consumers' success perceptions are, in turn, determined by their expectations of overall participation and efficacy, as well as the message frame inherent in proboycott communications. Two key determinants of consumers' boycotting costs are their preference for the boycotted product and their access to its substitutes. More specifically, consumers who are more susceptible to the normative influence exerted by the reference group of potential boycotters are more influenced by expected overall participation rates in their boycott likelihood.