Authoritarianism is a political system characterized by the rejection of political plurality, the use of strong central power to preserve the political status quo, and reductions in democracy, separation of powers, civil liberties, and the rule of law. Authoritarian regimes may be either autocratic or oligarchic and may be based upon the rule of a party, the military, or the concentration of power in a single person. States that have a blurred boundary between democracy and authoritarianism have sometimes been characterized as "hybrid democracies", "hybrid regimes" or "competitive authoritarian" states.

The political scientist Juan Linz, in an influential 1964 work, An Authoritarian Regime: Spain, defined authoritarianism as possessing four qualities:

Minimally defined, an authoritarian government lacks free and competitive direct elections to legislatures, free and competitive direct or indirect elections for executives, or both. Broadly defined, authoritarian states include countries that lack human rights such as freedom of religion, or countries in which the government and the opposition do not alternate in power at least once following free elections. Authoritarian states might contain nominally democratic institutions such as political parties, legislatures and elections which are managed to entrench authoritarian rule and can feature fraudulent, non-competitive elections.

Since 1946, the share of authoritarian states in the international political system increased until the mid-1970s but declined from then until the year 2000. Prior to 2000, dictatorships typically began with a coup and replaced a pre-existing authoritarian regime. Since 2000, dictatorships are most likely to begin through democratic backsliding whereby a democratically elected leader established an authoritarian regime.

Authoritarianism is characterized by highly concentrated and centralized government power maintained by political repression and the exclusion of potential or supposed challengers by armed force. It uses political parties and mass organizations to mobilize people around the goals of the regime. Adam Przeworski has theorized that "authoritarian equilibrium rests mainly on lies, fear and economic prosperity."

Authoritarianism also tends to embrace the informal and unregulated exercise of political power, a leadership that is "self-appointed and even if elected cannot be displaced by citizens' free choice among competitors", the arbitrary deprivation of civil liberties and little tolerance for meaningful opposition. A range of social controls also attempt to stifle civil society while political stability is maintained by control over and support of the armed forces, a bureaucracy staffed by the regime and creation of allegiance through various means of socialization and indoctrination. Pippa Norris and Ronald Inglehart identify authoritarianism in politicians and political parties by looking for values of security, conformity, and obedience.

Authoritarianism is marked by "indefinite political tenure" of the ruler or ruling party (often in a one-party state) or other authority. The transition from an authoritarian system to a more democratic form of government is referred to as democratization.

Authoritarian regimes often adopt "the institutional trappings" of democracies such as constitutions. Constitutions in authoritarian states may serve a variety of roles, including "operating manual" (describing how the government is to function); "billboard" (signal of regime's intent), "blueprint" (outline of future regime plans), and "window dressing" (material designed to obfuscate, such as provisions setting forth freedoms that are not honored in practice). Authoritarian constitutions may help legitimize, strengthen, and consolidate regimes. An authoritarian constitution "that successfully coordinates government action and defines popular expectations can also help consolidate the regime's grip on power by inhibiting re coordination on a different set of arrangements." Unlike democratic constitutions, authoritarian constitutions do not set direct limits on executive authority; however, in some cases such documents may function as ways for elites to protect their own property rights or constrain autocrats' behavior.