Aggressive and antisocial acts need to be prevented because (1) they cause serious problems to the individuals who are at the receiving end, (2) they lead to fear and escalation in the community, and (3) they often indicate that the offender has a history of mental health problems. Physical aggression and many other forms of antisocial behavior appear during the first few years after birth. Although most learn to regulate them by the time they enter the formal school system, a substantial minority of children do not. This lack of socialization on their part often has important consequences well into adulthood. This chapter will not only review studies of antisocial behaviors globally, but will focus on subtypes of conduct disorder. Indeed, although there may be commonalities between antisocial behaviors, these may not necessarily follow the same developmental course, share the same correlates, or develop jointly. Further, these may be manifested differently in boys and girls. It is only with a better understanding of these developmental factors that we may improve the effectiveness of prevention and corrective interventions.