The present article reports a longitudinal study of the psychological antecedents for, and outcomes of, collective action for a community sample of activists. At Time 1, activist identification influenced intentions to engage in collective action behaviours protesting the Iraq war, both directly and indirectly via perceptions of the efficacy of these behaviours for achieving group goals, as well as perceptions of individual-level benefits. At Time 2, identification was associated with differences in the dimensions on which the movement's success was evaluated. In the context of the movement's failure to achieve its stated objectives of troop withdrawal, those with strong activist identity placed less importance on influencing government decision making. The implications are discussed in terms of models of collective action and social identity, focusing on a dynamic model that relates identification with a group to evaluations of instrumentality at a group and individual level; and to beliefs about strategic responses to achieve group goals.