Instances of group behavior and group violence share the characteristic of swarming behavior, which is defined as “the unexpected gathering of large numbers of people in particular public locales.” Swarming may or may not involve violence but it does involve large crowds that have the capacity to transform into mobs. Different types of group formations and group behaviors are identified and described, including raves, flash mobs, youth gangs, riots, mobs, and gatecrashers. The relationship between rituals and group violence is examined. Rituals are linked with specific types of group violence, such as police baiting, as well as with the rule of engagement of specific types of group violence. For example, rituals of gang violence dictate that restraint must be shown when violently engaging a fellow gang member. Commonalities have been identified across the events and groups associated with violence and include: (1) the active use of new communication technologies, such as mobile phones, combined with access to motor vehicles; (2) an emphasis on excitement and taking control over certain areas; (3) defiance to authority figures; (4) an element of unpredictability due to the diversity and anonymity of participants; and (5) the role of the media in reflexively creating violent events by publicizing them in advance. Police intervention strategies for group violence are reviewed. Police may chose to institute coercive measures to deal with problematic groups, such as targeting identified youth gangs or targeting specific locations where group violence frequently occurs. More passive approaches may also be considered in certain situations, such as when the group violence is specifically targeted at eliciting a police response. Community policing strategies for dealing with group violence are highlighted and have the benefit of improving relations between the police and potentially problematic groups. Practical crime prevention strategies for swarming types of events are offered. References