Since 2001, violent sub-national groups with disparate ideologies and motivations have been working together to further their objectives. They are collaborating, sharing each others tactics, and learning from one anothers successes and failures. What is the background or historical context of the crime-terror nexus, and what challenges does it present to U.S. homeland security practitioners This thesis uses a case study approach to examine the history of the nexus between transnational criminal organizations and foreign terrorist organizations. The three case studies are then used as the data for the analysis chapter, which shows the historical and emerging relationships between states and the three violent sub-national groups. The three case studies suggest the activities of these violent sub-national groups are protean in nature they are best described by analysts as falling into the gray area phenomenon. The three case studies, the analysis, and conclusion of this thesis support the recommendation that more effort needs to be placed on intelligence collection, especially at the domestic and local levels.