Most discussions of the so-called crime-terror nexus revolve around a very simple observation: terrorists and insurgents frequently engage in criminal activity as a source of revenue. There is no question that crime has been and continues to be a lucrative source of funding for all kinds of terrorists. However, there is still ongoing disagreement about the extent of overlap between the worlds of terrorism and organized crime (OC). Often there is a tendency to over-generalize from specific cases, to speculate or, at times, to overlook the available evidence. Confusion over the nature of the threat in turn acts as a barrier to developing more effective countermeasures. Based on a combination of the authors’ engagement with academic literature on the subject and operational experience, this chapter begins by examining the similarities and differences between terrorists and criminals including profiles, methods, systems of organization, and motives. In other words, the who, what, how and why of terrorism and OC. This is followed by a discussion of the crime-terror nexus and the concept of “convergence,” i.e. the relationships between terrorism and crime. The chapter then concludes with a brief discussion of implications for counter-terrorism (CT) and law enforcement (LE).