Hegemony ( (listen), UK also , US also ) is the political, economic, and military predominance of one state over other states. In Ancient Greece (8th c. BC – AD 6th c.), hegemony denoted the politico-military dominance of the hegemon city-state over other city-states. In the 19th century, hegemony denoted the "social or cultural predominance or ascendancy; predominance by one group within a society or milieu" and "a group or regime which exerts undue influence within a society".

In theories of imperialism, the hegemonic order dictates the internal politics and the societal character of the subordinate states that constitute the hegemonic sphere of influence, either by an internal, sponsored government or by an external, installed government. The term hegemonism denoted the geopolitical and the cultural predominance of one country over other countries, e.g. the hegemony of the Great Powers established with European colonialism in Africa, Asia, and Latin America.

In Marxist philosophy, Antonio Gramsci defined cultural hegemony as the ruling class's domination of the value system and mores of a society, so that the ruling class perspective is imposed as the world view of society; thus, in the relations among the social classes of a society, the term hegemony describes the cultural dominance of a ruling class, which compels the subordination of the other social classes.

In International Relations, hegemony is the only great power in a unipolar system. Its military power is of such capability that no other state has the wherewithal to put up a serious fight against it; its economic power is of the same magnitude, and it is ambitious and willing to impose a certain order on the international system.