Whether exposure to violence in the virtual reality of the media has an impact on users' aggressive behaviour has been a controversial issue in academic as well as public debate. This article summarises a programme of research conducted with adolescents in Germany that presents cross-sectional and longitudinal evidence for the association between violent media use and aggression. It provides experimental evidence in support of mediating variables, such as hostile attributional style, increased normative acceptance of aggression, and emotional desensitisation, which might explain the pathways from media violence use to aggression. In addition it presents the development and experimental evaluation of a theory-based intervention designed to reduce media violence use and decrease its link with aggressive behaviour. The findings are discussed in the context of a large international body of research that points to the causal role of violent media use as a risk factor for aggressive behaviour.