Second Step is a social-emotional, skill-based, violence-prevention programme, which has been adapted for several European countries. The various versions of the programme (for kindergarten/preschool, elementary school, middle school) have been evaluated in a series of research studies. The outcomes and study designs of these studies are reported in this overview, proving that Second Step is effective in reducing aggressive behaviour and promoting social-emotional skills in children and adolescents. As examination of the European programme versions show, the effectiveness of the programme is upheld when the original programme is adapted.