Bullying is repetitive aggressive behaviour with an imbalance of power. Research, especially on school bullying, has increased massively in the last decade, fuelled in part by the rise of cyberbullying. Prevalence rates vary greatly. This is in part because of measurement issues, but some persons, and groups, are more at risk of involvement. Victims suffer from bullying, but some of those who perpetrate bullying can be socially skilled and get at least short-term benefits from their behaviour. Individual, family, school class, school and broader country factors can inf luence the chances of involvement. Beyond individual coping strategies, there have been many anti-bullying interventions developed over the last 30 years. Metaanalyses of these programmes show that they have had some success. Further progress is needed in establishing the most effective components and in tackling cyberbullying.