The purpose of this report is to use data from a sample of recently booked arrestees in Maricopa County to examine the scope and nature of Maricopa County’s gang problem. In particular, this report supplements data presented in the bi-annual report on gangs conducted by the Arizona Criminal Justice Commission, which relies on official police data and their occasional white paper on gangs that relies on self-report data from school youth. We organized our analyses around six research questions: (1) what proportion of adult arrestees are involved in a gang, and what are the socio-demographic differences between those who are associated with a gang and those who are not; (2) what are the rituals associated with gang joining; (3) how do gang and non-gang arrestees differ in their experiences with crime, drug use and victimization; (4) what is the organizational structure and composition of gangs; (5) how do members socially identify with their gang; and (6) how and why do members leave their gang?