This chapter examines the research on gangs and violence, noting important trends about the spatial distribution of gangs in cities, the role of social networks in gang violence, and the influence of gang culture on potentially violent interactions between gangs. The image of a violent gang or gang member is common in popular culture, news media, political arenas, and law enforcement circles. Gang violence is clustered within social networks and moves through both those networks and physical space, similar to an infectious disease. Gang life involves a complex negotiation of interpersonal and group dynamics during social interactions in public settings. To survive, thrive, or even dominate the social situation, gang members, or other participants of street life, may work to develop a reputation for violence. Violence is not only transmitted across networks through street socialization, but also through repetitious interactions between conflicting parties that can escalate when a single violent incident leads to more intense violence.