Objective: Little systematic research has focused on motivations for aggression, and most of the existing research is qualitative and atheoretical. This study increases existing knowledge by using the theory of coercive actions to quantify the apparent motives of individuals involved in barroom aggression. Objectives were to examine: gender differences in the use of compliance, grievance, social identity, and excitement motives; how motives change during an aggressive encounter; and the relationship of motives to aggression severity. Method: We analyzed 844 narrative descriptions of aggressive incidents observed in large late-night drinking venues as part of the Safer Bars evaluation. Trained coders rated each type of motive for the 1,507 bar patrons who engaged in aggressive acts. Results: Women were more likely to be motivated by compliance and grievance, many in relation to unwanted sexual overtures from men, whereas men were more likely to be motivated by social identity concerns and excitement. Aggressive acts that escalated tended to be motivated by identity or grievance, with identity motivation especially associated with more severe aggression. Conclusions: A key factor in preventing serious aggression is to develop approaches that focus on addressing identity concerns in the escalation of aggression and defusing incidents involving grievance and identity motives before they escalate. In bars, this might include training staff to recognize and defuse identity motives and eliminating grievance-provoking situations such as crowd bottlenecks and poorly managed queues. Preventive interventions generally need to address more directly the role of identity motives, especially among men.