While research has consistently found evidence for the impact of taxpayers' personal norms (individual ethics and morality of tax paying) on levels of tax compliance, findings for the role of social norms (ethics and morality attributed to other taxpayers) on tax compliance have been more ambiguous. The present paper argues for a theoretically more refined analysis of norm processes, based on self-categorisation theory. Specifically, social norms should elicit concurring behaviour when taxpayers identify with the group to whom the norms are attributed; they then internalise the social norms and act accordingly. In contrast, social norms should be ineffective when identification is weak; social norms might then even backfire when they contrast with one's internalised norms. Data from a survey with Australian citizens (listwise N=1306) yielded empirical support for these predictions. Limitations and implications of the study are discussed.