In political science, legitimacy is the right and acceptance of an authority, usually a governing law or a regime. Whereas authority denotes a specific position in an established government, the term legitimacy denotes a system of government—wherein government denotes "sphere of influence". An authority viewed as legitimate often has the right and justification to exercise power. Political legitimacy is considered a basic condition for governing, without which a government will suffer legislative deadlock(s) and collapse. In political systems where this is not the case, unpopular regimes survive because they are considered legitimate by a small, influential elite. In Chinese political philosophy, since the historical period of the Zhou dynasty, the political legitimacy of a ruler and government was derived from the Mandate of Heaven, and unjust rulers who lost said mandate therefore lost the right to rule the people.

Authority is commonly understood as the legitimate power of a person or group over other people. In a civil state, authority is practiced by the legislative, executive, and judicial branches of government. The term authority has many nuances and distinctions within various academic fields ranging from sociology to political science.