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Bullying is an insidious form of violence that develops in the intimacy of social relationships. It may appear in all social contexts at any age and whatever the cultural levels of the actors. In this article the main topics of research associated with bullying are presented. The papers of this thematic issue deal with the development of aggression related to social development, the specificity of school bullying, the various strategies of bullying and in particular cyberbullying. The issue also includes analyses of the characteristics of bullies and witnesses and finally presents a prevention program.