In politics, a regime (also spelled régime) is a system of government that determines access to public office, and the extent of power held by officials. The two broad categories of regimes are democratic and autocratic. A key similarity across all regimes is the presence of rulers of both formal and informal institutions, which interact dynamically to adapt to changes to their environment. The CIA World Factbook also has a complete list of every country in the world with their respective types of regimes.

According to Yale professor Juan José Linz there are three main types of political regimes today: democracies, totalitarian regimes, and authoritarian regimes, with hybrid regimes sitting between these categories.

The term regime is often used critically to portray a leader as corrupt or undemocratic. While the term originally referred to any type of government, in modern usage it often has a negative connotation, implying authoritarianism or dictatorship. Merriam-Webster defines a regime simply as a form of government, while the Oxford English Dictionary defines it as "a government, especially an authoritarian one."

In contemporary academic discourse, the term "regime" is used more broadly than in popular or journalistic contexts. It refers to "an intermediate stratum between the government, which is responsible for day-to-day decision-making and can be changed relatively easily, and the state, which encompasses a complex bureaucracy tasked with a wide range of coercive and administrative functions." In global studies and international relations, the concept of regime is also used to name international regulatory agencies (see International regime), which lie outside of the control of national governments. Some authors thus distinguish analytically between institutions and regimes while recognizing that they are bound up with each other:

Institutions as we describe them are publicly enacted, relatively-enduring bodies of practice, procedures and norms, ranging from formalized legal entities such as the WTO to more informal but legally-buttressed and abiding sets of practices and regimes such as the liberal capitalist market. The key phrases here are 'publicly enacted' and 'relatively enduring'. The phrase 'publicly enacted' in this sense implies active projection, legal sanction, and often as not, some kind of opposition.

Regimes can thus be defined as sets of protocols and norms embedded either in institutions or institutionalized practices – formal such as states or informal such as the "liberal trade regime" – that are publicly enacted and relatively enduring.It is common to tie an individual or ideology to a government regime i.e. Putin's regime in Russia or China's Communist regime.

Authoritarian regimes are systems in which power is highly centralized, and often concentrated in the hands of a single leader or a small elite group. In authoritarian regimes, political opposition is often suppressed, with dissenting voices silenced through tactics such as censorship, imprisonment, or violence. Political freedoms, including freedom of speech and the press, are usually restricted or tightly controlled by the government. While elections may occur in some authoritarian systems, they are frequently neither free nor fair, with outcomes manipulated to secure the dominance of the ruling elite and maintain their hold on power. Political scientist Juan Linz states that an authoritarian government lacks both political pluralism and political mobilization. He states that an authoritarian regime specifically has vague limits on executive power in order to give more control to the executive branch.

For instance, Russia, since the Russian Revolution in 1918, holds elections, but these are heavily controlled, with significant restrictions placed on opposition parties and candidates, and media outlets operating under state influence. This demonstrates characteristics of authoritarianism.