This article introduces the concept of collective narcissism--an emotional investment in an unrealistic belief about the in group's greatness--aiming to explain how feelings about an ingroup shape a tendency to aggress against outgroups. The results of 5 studies indicate that collective, but not individual, narcissism predicts intergroup aggressiveness. Collective narcissism is related to high private and low public collective self-esteem and low implicit group esteem. It predicts perceived threat from outgroups, unwillingness to forgive outgroups, preference for military aggression over and above social dominance orientation, right-wing authoritarianism, and blind patriotism. The relationship between collective narcissism and aggressiveness is mediated by perceived threat from outgroups and perceived insult to the ingroup. In sum, the results indicate that collective narcissism is a form of high but ambivalent group esteem related to sensitivity to threats to the ingroup's image and retaliatory aggression.