For many decades communities have been troubled by the criminal activities of youth gangs. This report looks at almost 30 years of information collected on gang problems in nearly 4,000 communities. The number of localities reporting gang problems increased between the 1970s and the 1990s, representing a tenfold increase in the number of cities and elevenfold increase in the number of counties reporting problems. By the late 1990s, all 50 states and the District of Columbia had reported gang problems and the problems were widely spread throughout small and large cities. The states with the largest number of problem cities were California, Illinois, Texas, Florida, and Ohio. The data provide support for the prediction that the rate of gang activity growth will decrease in the early 2000s, and some support for the prediction that the actual number of gang localities will decrease. Sections are included on the scope of gang growth over the decades; location of gang growth; trends in gang cities; and an update of selected data. Reasons for the increase in the number of gang-problems are attributed to many factors including drugs; immigration; gang names and alliances; migration; government policies; female-headed households; and gang subculture and the media. (Contains 5 appendixes, 37 tables, 22 figures and 55 references.) (Author/JDM)