Fascism is a far-right, authoritarian, ultranationalist political ideology and movement, characterized by a dictatorial leader, centralized autocracy, militarism, forcible suppression of opposition, belief in a natural social hierarchy, subordination of individual interests for the perceived good of the nation and race, and strong regimentation of society and the economy.

Fascism rose to prominence in early 20th-century Europe. The first fascist movements emerged in Italy during World War I, before spreading to other European countries, most notably Germany. Fascism also had adherents outside of Europe. Opposed to anarchism, democracy, pluralism, liberalism, socialism, and Marxism, fascism is placed on the far-right wing within the traditional left–right spectrum.

Fascists saw World War I as a revolution that brought massive changes to the nature of war, society, the state, and technology. The advent of total war and the mass mobilization of society erased the distinction between civilians and combatants. A military citizenship arose in which all citizens were involved with the military in some manner. The war resulted in the rise of a powerful state capable of mobilizing millions of people to serve on the front lines and providing logistics to support them, as well as having unprecedented authority to intervene in the lives of citizens.

Fascism rejects assertions that violence is inherently bad and views imperialism, political violence and war as means to national rejuvenation. Fascists often advocate for the establishment of a totalitarian one-party state, and for a dirigiste economy, with the principal goal of achieving autarky (national economic self-sufficiency) through protectionist and economic interventionist policies. Fascism's extreme authoritarianism and nationalism often manifests as belief in racial purity or a master race, usually blended with some variant of racism or bigotry against a demonized "Other", such as Jews. These ideas have motivated fascist regimes to commit genocides, massacres, forced sterilizations, mass killings, and forced deportations.

Since the end of World War II in 1945, few parties have openly described themselves as fascist; the term is more often used pejoratively by political opponents. The descriptions of neo-fascist or post-fascist are sometimes employed to describe contemporary parties with ideologies similar to, or rooted in, 20th-century fascist movements. Some opposition groups have adopted the label anti-fascist or antifa to signify their stance.