Law enforcement agencies continue to be the best and most widely used source of information for national gang surveys and other forms of criminal justice research. Criminal justice agencies usually are organized centrally and capable of developing systems for routine recordkeeping and reporting (Curry, 1995; Maxson, Klein, and Cunningham, 1993). However, law enforcement data have some important limitations. First, many agencies do not collect data in a standardized manner. Databases are becoming more widespread, but they are more commonly used for intelligence gathering than for crime recording. Second, law enforcement agencies are sometimes affected and constrained by political considerations, and a gang problem may tend to be either denied or exaggerated (Curry, 1995). Third, agencies, and individuals within agencies, often have differing definitions of what constitutes a gang or a gang incident, and perceptions of the problem vary depending upon the expertise and experiences of the observer. Varying definitions in different jurisdictions continue to be problems for the collection of gang data.