Infants develop the capacity to use force against other people in the first years of life, which gradually transforms into intentional aggression, particularly as they understand possession rights. Individual differences in expressing anger and using force are evident from 6 months and predict later aggressive conduct problems. In contrast, gender differences emerge gradually over early childhood. Toddlers' sparing use of force in interactions with other children is linked to other forms of sociability, but excessive rage and using physical force in infancy predict problematic levels of aggressiveness in later childhood. Acknowledging the early origins of aggression can inform prevention and intervention strategies.