The termination of the Cold War brought about dynamic and deep changes in the global system parameters: (1) bipolar global structure has been replaced by a mix of monopolar and multipolar ones; (2) in international relations, the role of a state has become less and the role of nonstate subjects more important; (3) security competition has been replaced by security cooperation, and the "security dilemma" - by promulgating the trust; (4) the implication of the "hard power" has become equal with that of the "soft power" (the military power with the non-military power forms); (5) conventional military threats (of military conflicts between states) have diminished, and new types of threats (so-called asymmetric threats) have grown; (6) regional security-defense organization have turned into the security communities (static military alliances into dynamic partnerships). National security increasingly relies directly on the joint (collective) security and the security of an individual; (7) authoritarian socialist regimes (especially in East Europe) have been replaced by democracies; (8) directed economies and closed markets have been replaced by liberal economies and open markets, etc. Such deep changes have unavoidably led to questioning of theoretical patterns of the social sciences and opened "broad avenues" to new considerations in all areas, particularly in the science of international relations and security. Knowledge of contemporary trends in theoretical thinking within these two important areas is necessary today for all social entities concerned with the occurrences in international relations and security. First, without knowing them it is impossible to understand dynamic social occurrences in the contemporary world, and second, it is a prerequisite for an evaluation of future development of social practice and consequently, for guidance of social action towards the desired objective. This short study puts an emphasis primarily onto theoretical considerations of international relations, which have already been, or are becoming increasingly applied in the international practice, at the turn of the millennium.