The social psychological definition of groups implies that criminal gangs, like other groups, involve more than a collection of people who engage in antisocial behavior. One of the necessary aspects of a gang includes how the members perceive the meanings and missions of the gang and the significance the individual gang members attach to the membership. Gangs affect individual members' motivations by meeting and sustaining their individual members' needs for social identity. Also, a group's norms, rules, and moral standards justify the actions of its individual members, particularly when these actions conflict with some established social norms. A gang affects its individual members' cognition through the majority-imposed informational influence, which makes gang members believe that the perceptions of the majority in the group must be correct. A group can also produce the diffusion of responsibility and deindividuation. This involves a loss of personal responsibility for individual actions and less concern about the consequences. The author also argues that gang members are more vulnerable to group influences than other juveniles because they are isolated from other social environments and are more likely to have experienced various criminogenic influences, such as violent victimization, unemployment, and limited education. 40 references