Street gangs have exploded in popularity worldwide. Tattoos, baggy pants, tagging, gangsta style clothes -- this unspoken threat is always just around the corner in most of the world's major cities. In search of a sense of identity and belonging that their world has denied them, young people are pushed into gangs by a witch's brew of violence, guns, drugs, racism, poverty, families under pressure, and ever-widening slums. "Gangs" exposes the roots of the problem, from the "bidonvilles" of France to the "favelas" of Brazil. It offers a startling analysis of the complicity of the adult world, as well as hard-hitting reforms that might just undermine the appeal of gang life. Most of all, it shows that we fail to understand gangs at our peril.