Inappropriate aggression and violence is a pervasive feature of contemporary society. The great advances in the authors' knowledge of brain function have helped our understanding of the neural mechanisms underlying behaviour. This chapter focuses on what the authors know of these as they apply to aggression. It is axiomatic that the brain plays a central role in aggression, both by recognizing aggression-provoking stimuli, and formulating aggressive responses. The regulation of aggression is a distributed function of the brain. There are many anatomical areas associated with aggression, though whether there are specific 'aggressive' nuclei remains doubtful. There are also a plethora of neurochemical systems implicated in aggression. The challenge to those studying aggression in children is to identify the interplay between specific genes and critical elements of the social and physical environment that, together, determine long-lasting patterns of aggressive behaviour.