Aggression involving groups (versus individuals) can be particularly severe (e.g., hazings). Although an impressive amount of experimental research on the aggression of individuals exists, relatively less experimental research on aggression involving groups exists. We use existing theories of aggression and the available research to present a framework of aggression when groups are involved. We propose a provisional model that suggests that the extent of aggression to be committed depends on the composition of both source (i.e., perpetrators – group or individual) and target (i.e., victims – group or individual) entities. Evidence suggests that groups commit and receive more aggression than individuals. We propose that accessible hostile thoughts and the experience of negative affect contribute to the target effect (i.e., more aggression committed toward groups versus individuals), whereas disinhibition processes and arousal contribute to the source effect (i.e., more aggression committed by groups versus individuals). Our framework can guide future theory and research on aggression involving groups.