Bullying represents a significant problem in U.S. schools, affecting approximately one in three children. The authors discuss the dynamics, types, characteristics, and consequences of school bullying. Risk factors for engaging in bullying, being bullied, and becoming both a bully and a victim are discussed. Research indicates that bullying has serious long-term negative effects on bullies, victims, and victims who turn to bullying as a coping strategy. Longitudinal relationships between childhood bullying and victimization and adult mental health outcomes such as anxiety, depression, substance use, and conduct disorders are outlined. Prevention programs, and their relative efficacy from empirical evaluations, are also presented. Finally, implications for school-based prevention services are provided.