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.

The right to exist is said to be an attribute of nations. According to an essay by the 19th-century French philosopher Ernest Renan, a state has the right to exist when individuals are willing to sacrifice their own interests for the community it represents. Unlike self-determination, the right to exist is an attribute of states rather than of peoples. It is not a right recognized in international law. The phrase has featured prominently in the Arab–Israeli conflict since the 1950s.