A questionnaire survey of 392 Illinois law enforcement agencies received responses from 341 agencies, about half of which reported street gang problems involving both adults and juveniles. The preponderance of this gang activity was in the northern part of the State, but gangs are present in urban, suburban, and rural areas. School districts throughout the State are experiencing gang recruitment. In addition, increasing numbers of students are being victimized. The crimes accompanying these gangs include drug law offenses, murders, sexual assaults, armed robberies, burglaries, and automobile thefts. A rapid and coordinated law enforcement response is needed, but almost 60 percent of the local and county police agencies responding to the survey have no officers assigned to gangs on either a full- time or part-time basis. In addition, a single agency cannot handle the problem on its own; agencies must cooperate closely to deal with gangs. Appended terminology, list of gangs, and samples of graffiti.