Increasingly, researchers are turning their attention to the issue of aggression and violence perpetrated by girls and women. This reflects mounting evidence from several related fields of research including: criminal justice, corrections, forensic psychology and psychiatry, domestic violence, child and elder abuse, and delinquency and juvenile justice. Together, this research supports several broad conclusions: (i) the assumption of female nonviolence is untenable; (ii) rates of female-perpetrated aggression are escalating; (iii) aggression by females often has serious negative implications for victims; and (iv) there is insufficient research of risk and protective factors, developmental trajectories, and clinical programs to prevent and reduce female aggression. In this paper, we report the prevalence and incidence of aggression among females; document sex differences and similarities in aggressive and violent behavior; and examine sex-specific versus common risk factors. We conclude with clinical implications for prevention and intervention and reflect on gaps in knowledge and directions for future research.