In the past, juvenile gang researchers have focused primarily on the characteristics of gangs and the prevalence of gangs in communities and schools. One of the greatest limitations of this research, however, surrounds the lack of agreement on the definition of a gang and, consequently, the prevalence of gangs in the community and in schools. In this paper, we attempt to provide a new method to (1) define a gang, from a triangulation of the perspectives of law enforcement, school principals, and gang researchers and (2) estimate the prevalence of gangs in schools in a three-state region. We determine that the type of definition used dramatically impacts estimates of the prevalence of gangs in schools. The limitations and implications of this finding for school administrators and law enforcement are also discussed. In the past, juvenile gang researchers have focused primarily on the characteristics of gangs and the prevalence of gangs in communities and schools. One of the greatest limitations of this research, however, surrounds the lack of agreement on the definition of a gang and, consequently, the prevalence of gangs in the community and in schools. In this paper, we attempt to provide a new method to (1) define a gang, from a triangulation of the perspectives of law enforcement, school principals, and gang researchers and (2) estimate the prevalence of gangs in schools in a three-state region. We determine that the type of definition used dramatically impacts estimates of the prevalence of gangs in schools. The limitations and implications of this finding for school administrators and law enforcement are also discussed. (Contains 2 tables and 3 notes.)