With the accelerated process of modernization the number of revolutions has increased. The 20 th century witnessed many events of this kind. The authors analyze the main features of the twentieth-century revolutions, and their difference from those of the 19 th century. In the 20 th century, revolutionary activities increasingly moved from the World System core to its semi-periphery or even to the periphery (in the 19 th century, though they often happened not in the core, but close to it, which sometimes allowed countries that survived the revolution to move to the core). As a result, the influence of revolutions on the historical process changed and their role as driving forces of progress in respect of the World System generally decreased. Also, guerilla warfare in the revolutionary societies of the periphery and semi-periphery became very common. New types of revolution emerged, and less widespread types further diffused. First of all, these were Communist revolutions, and toward the end of the century as a result of the decline of Communism -anti-communist ones as well as powermodernist and others. The authors offer a new typology of revolutions. The twentieth-century revolutionary process is described in chronological order as comprising four revolutionary waves and intervening periods (like the 1930s, or the 1950s -1970s) when revolutionary waves were not observed. Significant