After decades of neglect, researchers have begun to focus attention on the development and outcomes of girlhood aggression. This comprehensive volume provides an account of some of the pioneering research in the field. Its central aims are to highlight current understanding, identify key components for preventing and treating the complex array of problems experienced by aggressive girls, and raise new questions for future research. The perspectives presented by the authors highlight the diverse factors that moderate the emergence of aggression while offering insight into how to target that aggression at various stages of development. The problem is presented as a continuum from normative forms of behavior to extreme and serious attacks. The importance of relationships–particularly family relationships–is a theme that permeates the entire volume. A growing body of research indicates that aggression in girls is a predictor of long-term psychological, social, academic, health, and intergenerational problems. The knowledge provided by the authors has tremendous potential to inform practice with troubled girls, their families, and support systems.