Every year about 200.000 adolescents and young people between the ages of 10 and 29 die, which places homicide in fourth place in the world as cause of death in young population. Several million adolescents and young people suffer from acts of violence, and trauma that require urgent medical and psychological treatment. The emotional imprints that youth volence leaves on its survivors and their loved ones are often profound. Youth violence destroys lives and its consequences have very high economic costs, both for society and for the families of young people. The goal of this manual is to provide a scientific framework that allows us to understand why some people have a greater tendency to be involved in acts of youth violence and how to prevent it.