According to NATO, terrorists and organized crime groups work together every day in drugs, arms, cyber, and financial crime, and many other activities. They often share techniques, personnel, skills and knowledge in a time where the difference between these two groups is increasingly blurred. While both activities have existed for a very long time, there are some elements which facilitate the nexus between them. For example, we can talk about the globalization and the ability to move freely between states and across borders. The progress in technology and communications, the liberalization of markets, the decline of state sponsored terrorism since 9/11 forced terrorist groups to find new ways on funding, and they have met organized crime groups as their best partners. Finally, we may say that the Jihadist threat goes beyond the traditional terrorists model of organization based exclusively on hierarchical structures and an integrated and structured affiliation. However, before we move further on the topic, we should start providing a definition for both terrorism and serious organized crime. This is not an easy job, as they are complex phenomenon which have been explored by several disciplines like sociology, law, criminology, anthropology, and psychology among others. Therefore, we can probably find as many definitions as scholars interested in the topic. If we start with the concept of serious organized crime, one of the key documents is the UN Convention against Transnational Organized Crime, which entered into force on September 2003. Although it does not provide a definition of serious and organized crime as such, it states the key elements of an organized criminal group. According to article 2A, "Organized criminal group" shall me a structured group of three or more persons, existing for a period of time and acting in concert with the aim of committing one or more serious crimes or offenses, in order to obtain, directly or indirectly, a financial or other material benefit. Therefore, in this definition, we can find four criteria to establish what an organized criminal group is. First, it is a structured group of three or more persons. According to some authors, we must keep in mind that it is not the number of people what makes the concept of organized crime, but the organization and the internal and external coordination between them when they act. Second, the group must exist for a period of time. Therefore, and according to article 2C of the same convention, this shall mean a group that it is not randomly formed for the immediate commission of an offense, and does not need to have formally defined roles for its members, continue of its members shape or a developed structure. Third, the group must have the aim of committing one or more serious organized crimes or offenses. According to article 2B, a serious crime shall mean a conduct constituting an offense punishable by a maximum deprivation of liberty of at least four years or a more serious penalty. Fourth, they must have the aim to obtain, directly or indirectly, a financial or other material benefit. They can do it through a wide range of topology of crimes. More than one-third of the groups are involved in drug production, traffic, and distribution. But there are other types of illicit activities in which they might be involved such as fraud, migrant smuggling, organized property crime, trafficking of endangered species, of firearms, and human beings among others.