Aggressive behaviour is a common phenomenon during childhood and adolescence, but at the same time it is an important associated feature of many psychiatric disorders during this age period. Persistent aggression is related to a variety of negative outcomes in adulthood, including low socioeconomic status and unemployment, criminal behaviour and social isolation. The great heterogeneity of aggressive behaviour still hampers our understanding of causal mechanisms. Still, over the past years, the identification of specific subtypes of aggression has opened possibilities for new and individualized treatment approaches. This article provides information on different subtypes of aggression in children and adolescents, on individual differences that contribute to aggression during development and on possible underlying processes related to aggressive behaviour in young people. Current treatment approaches as well as new emerging treatment possibilities are discussed.