Aggression is any behavior that hurts another, whether physically or emotionally. The frustration-aggression hypothesis implies that the nature of the frustration influences the intensity of the resulting aggression. Two factors that intensify aggression are the strength and the arbitrariness of frustration. This chapter covers potential rewards, presence of models, norms, stress, and aggressive cues. Virtually every society has norms that approve aggression against particular targets in particular circumstances. Stress also increases the likelihood of aggressive behavior. Aggressive cues also affect aggression by a process of ruminative thought. The chapter discusses four target characteristics related to aggression: race and gender, attributions for the aggressor's attack, and retaliatory capacity. The relationship between aggression and gender depends on the type of aggressive behavior. Aggressive behavior is more likely if the target is of the same race or ethnicity. An important influence on attributions is whether an attacker apologizes.