An analysis of rich empirical material collected through periodic author studies of aggressive behavior and its social and personal determinants is presented. Changes in attitudes and readiness for aggression are tracked at the individual, social group, and supra-individual levels. General conclusions are proposed about aggression, which in the last ten years of the century has acquired the role and scale of a mass socio-psychological phenomenon. Tolerance towards violence, the desire for revenge, vindictiveness and resentment, as well as the mass perceptions among Bulgarians of the violence and aggression contained in the media are examined. Based on an analysis of contemporary trends in the socio-psychological study of aggression, an attempt is made to outline a new direction in the development of the theory of aggression.