Five independent studies were used to test the hypothesis that a reliable 2-factor structure underlies the Reactive-Proactive Aggression Questionnaire (RPQ) items and that the 2 scales show distinct patterns of association with personality and bullying behavior measures. Study 1 (N = 1,447) gave evidence of a clear 2-factor structure of RPQ items with factor loading matrices closely matching reactive (congruence coefficient = .90) and proactive (congruence coefficient = .91) models of item assignment. The RPQ 2-factor structure was consistently replicated in Study 2 (N = 662), as well as across the remaining 3 studies. In Study 3 (N = 536), Neuroticism differentiated reactive and proactive forms of aggression. In Study 4 (N = 674), self-reports of bullying behaviors were selectively correlated with proactive aggression. Findings confirm and extend the differential correlates of proactive-reactive aggression and also support the psychometric properties of the RPQ in a different cultural context. Finally, in Study 5 (N = 347), the RPQ scales showed adequate 2-month test-retest reliability. (PsycINFO Database Record (c) 2009 APA, all rights reserved).