"Bullying" involves aggressive behavior or intentional harms by a person or group against other persons; a repetition of these actions over time; and an imbalance of power. A survey conducted by the Federal National Institute of Child Health and Human Development in 1998 found that just under one-third of U.S. students in grades 6 through 10 were involved in moderate or frequent bullying. A characteristic found in all bullies is an inability to channel anger or frustration in an acceptable way. The victims of bullies tend to have a physical or personality characteristic that makes them different from most students, and they are usually physically small, weak, or otherwise vulnerable. Victims of bullying may also become bullies themselves. Theories on the causes of bullying focus on the behavior of dominating those who are different and weaker than oneself; the existence of social groups with different power status; peer pressure; and a failure to become integrated into positive school activities. Models for bullying prevention and intervention have the following features: creation of a school environment that accepts diversity and includes adult involvement in school activities; a clear statement and enforcement of unacceptable behavior at school; the application of consistent sanctions when infractions occur; and the existence of clear strategies for school staff in detecting and intervening when bullying occurs. Four promising prevention and intervention programs are described. Research has shown that comprehensive, schoolwide programs have been the most effective. Some features of State laws that address bullying are also outlined. The article concludes with a listing of 20 "best practices" for preventing discipline problems and bullying at school.