Prospective links among reactive aggression, proactive aggression, and victimization by peers were investigated in a longitudinal sample of 238 preadolescents (aged 10–13 years, 52% girls). No predictive links were found between victimization and either type of aggression among girls. Among boys, reactive aggression predicted higher future levels of victimization but was not itself affected by prior victimization. In contrast, boys' proactive aggression predicted lower levels of future victimization and was itself reduced by their prior victimization. Finally, reactive aggression predicted later proactive aggression for both boys and girls. These results are explained in terms of the different reactions that others have to proactive and reactive aggression, the different functions they serve, and to the different types of aggression that are common for boys and girls. Aggr. Behav. 33:1–9, 2007. © 2007 Wiley-Liss, Inc.