Bullies and their victims are more likely to engage in violent behavior than those who have never been involved in bullying. In both aggressor and victim, bullying is a sign of potential psychiatric disorder. It is primarily physical in children, becomes relational aggression in adolescents, and often appears in the form of sexual harassment in adulthood. The causes of bullying include the desire to control, revenge, envy, and emotional distress. Bullies have often themselves been bullied. Teachers are frequently reluctant to report bullying, even if they view it as a problem. Bullying deprives children of safety and security, but prevention and intervention are all too often not part of school curricula. The unique characteristics of bully and victim, risk factors leading to bullying behavior, the influence of the parents, and the roles of gender relationships and sex differences are explored in this article.