Urban violence sheds light on a paradox affecting cities on a global scale: contemporary urban life is about plurality and coexistence in globally connected spaces but is also frequently affected by violence that fragments the urban space along invisible borders, competing armed actors, safe and unsafe zones. Violence and insecurity are not equally distributed along the urban space but cluster in certain areas that become stages for disputes for local political and economic control: nonstate actors providing security (often linked to extortion rackets), criminal groups controlling illicit economies, politically connected militias vying for power, and rival communities competing for space or resources. This chapter identifies a common mechanism driving urban armed violence: the intensification of boundaries and political identities that divide the urban space. This fragmentation breaks down the flow of people, products, and information that characterize contemporary cities. It also reflects a fragmentation of state institutions and political authority at the local level, tying vulnerable communities to the whims of predatory actors in situations of armed conflict, intercommunity tensions, and organized crime. Despite the varying ways urban violence manifests, identifying common mechanisms through which violence emerges in cities can help communities and authorities collaborate and respond.