The subject of this paper is one of the most frequently used and least clarified notions in foreign affairs and the theory of international relations: the notion of security. It is most often found in discussions of the problems of the internal stability of political systems, protection of sovereignty, provision of peace and development and in discussions of the interests in disarmament. Public security means pro-vision of law and order and prevention of crime and terrorism, while state security implies provision of the continuity of the political system and constitutional government. National security is defined as an effort of every nation/state to preserve its sovereignty, territorial integrity, physical existence of its population, political independence and a right to development. Regional security is determined by the total political, ideological, economic and other relations in the region as well as by the interests of the great powers. International security is not a mere summation of the national security of individual countries but rather a commitment to appropriate values in international relations. Collective security is an instrument for the protection of the regional and international security. The author pays special attention to the security of developing countries as a separate model in international relations.