Aggressive behaviors have large social consequences among all species. Aggression may serve to protect one's vital concerns, disrupt relations, and command dominance or subordination and may be a strong source of admiration or rejection (e.g., Aureli & de Waal, 2000). Because of its social importance, multiple biological and cultural mechanisms to regulate aggression have evolved over time, including emotion processes that are key agents in the regulation of aggression, both within and between persons. Humans and other animals are highly sensitive to signals of others' emotional states. Processing of such emotion signals directly affects the perceiver's own emotional state, predisposing both body and mind to respond appropriately. These processes appear partly "hardwired" in the lower brain regions, but they also have an important socially regulated side, in which humans are highly sensitive to the social norms and conventions concerning emotional behavior and the meaning of emotion signals in social interactions (Dodge, 2006;Frijda, 1988).These emotion processes appear to be very relevant to our understanding of aggressive behavior problems in children. Could it be that aggressive behavior problems are triggered by dysregulation of emotional processes in social interaction? Can aggressive behavior problems result from lessened sensitivity