Street gangs have long been a concern to policy makers. The more recent emergence, growth, and expansion of two Latino street gangs, the Mara Salvatrucha (MS-13), and the 18th Street Gang, have raised concern among policy makers for several reasons. Reports suggest that these gangs are engaged in criminal enterprises normally associated with better organised and more sophisticated crime syndicates and perhaps most disturbingly for policy makers in a post 9/11 world, alarms have been sounded in some circles that international terrorist organisations like al-Qaeda could exploit alien and narcotics smuggling networks controlled by these gangs to infiltrate the U.S. This book provides an overview of the MS-13 and M-18 gangs, examines how these gangs are different from other gangs and organised crime groups, discusses what constitutes a transnational gang and the various federal responses to these gangs.