This study investigated the structure and concurrent validity of the Beliefs About Fighting Scale (BAFS). Participants were 2,118 students from three urban middle schools who completed measures of their beliefs, frequency of physical aggression, victimization, and nonviolent intentions. Ratings of students' frequency of physical aggression, physical victimization, and nonviolent behavior were also obtained from their teachers. The majority of the sample was African American (81%). Confirmatory factor analyses supported a model with separate factors representing beliefs against fighting, beliefs that fighting is sometimes necessary, beliefs supporting reactive aggression, and beliefs supporting proactive aggression. Support was also found for strong measurement invariance across sex, grade, and groups that differed in whether a violence-prevention program was being implemented at their school. The four BAFS factors were associated with adolescents' frequency of aggression, victimization, and nonviolent behavior. This study underscores the importance of assessing multiple aspects of beliefs associated with aggressive behavior.