Youth gang membership is associated with delinquency, violent crime and trafficking – and gang members are themselves frequently the victims of these offences. Yet youth gangs can also provide a form of social capital, a sense of belonging and purpose to disenfranchised youth. This review identifies the factors associated with young people joining gangs, and the differences between gang-involved and non-gang-involved youth. Understanding these associations is essential to reduce the levels of gang membership and the incidence of related violence