It is well established that only a very small proportion of children become persistently serious delinquents or adult psychopaths. Also, many boys and girls showing some aggression and disruptive behavior in earlier childhood will not progress to more serious conduct problems by adolescence. Thus, the study of conduct problems and serious outcomes requires knowledge of the age-normative problem behaviors and their course over time for boys and girls, and why some children and youth deviate from these normative patterns. The pattern, developmental course, and their causes are somewhat different for girls compared to boys, which is the main topic of this chapter. For example, most of the violence committed by adolescent girls, in contrast to boys, is directed at relatives, especially their mother or a dating partner. Assault rates by girls have increased over the years, but it is debatable to what extent these increases are a result of improved police work, and prosecution, and the reporting of simple assaults by the police (Zahn, 2007).