Recent accounts of collective action highlight the importance of psychological empowerment, but conceptualize it simply as a precondition for such action. By contrast, the social identity model (Reicher, 1996, 1997; Stott, 1996) suggests that empowerment is a product as well as a precondition of collective action. However, existing research on the social identity model has merely inferred the emergence of feelings of power rather than shown it empirically. This paper describes a study of a town hall anti-poll tax demonstration, using interviews, written accounts, newspaper accounts, and video evidence. The principal source consisted of interviews with 29 protesters which were subjected to thematic analysis to identify (i) whether and to what extent empowerment took place in the crowd; (ii) features of the intergroup relationship responsible for any such empowerment; and (iii) any normative limits to empowered behavior. The analysis suggests that feelings of power increased among crowd members due to the more inclusive categorization among them brought about by their perceived wholesale illegitimate exclusion from the town hall. Moreover, the empowered action of crowd members was limited by shared definitions of proper practice. The implications of these findings are discussed for studies of collective action, and it is suggested that further research along the present lines is necessary to shed more light on factors leading to the endurance and generalization of the types of empowerment found here.