This article reviews recent attachment-related studies of early aggression. That aggressive behavior toward peers is related to disorganized or controlling patterns of attachment behavior toward parents but not to avoidant or ambivalent patterns. Longitudinal attachment studies indicate that risk factors identified in cross-sectional studies of aggressive school-age children, such as family adversity, parental hostility, parental depression, and child cognitive deficits, are already evident in infancy and predictive of later aggression, before the onset of coercive child behavior. In infancy, these risk factors are associated with disorganized attachment behaviors toward the caregiver characterized by signs of fear or dysphoria, irresolvable conflict between opposing behavioral tendencies, and elevated cortisol levels after separation. Disorganized attachment behaviors, in turn, predict aggression in school-age children with other family factors controlled.