While in the post-Cold War era threats to international security have become less direct and apocalyptic, they are today more diffuse and insidious. With the probability of large scale, high intensity conflicts decreasing during the l990s, terrorism and transnational organized crime --each in itself-- constitute an increasing and serious threat to the national security of affected nations. Any alliance of these two criminal phenomena is likely to cause a disproportional increase of the overall threat. The thesis, while following an analytical/inductive approach, tries to identity the rationale for such alliances. Although aims and objectives of terrorists and organized criminal groups are different by nature, alliances of convenience have already formed in the past. With globalization apparently working in the favor of terrorists and organized crime, it seems to be only a question of time before they begin merging and start working jointly. Since those criminal organizations tend to exploit the weaknesses of international cooperation by increasingly operating in the transnational sphere, any attempt at a successtul counter-strategy has to meet this threat where it originates. Against this background, international cooperation of law enforcement agencies becomes increasingly important - "Internal Security", it seems, acquires a transnational dimension.