The Algerian War, also known as the Algerian War of Independence or in French: Guerre d'Algérie, was a conflict between France and Algerian independence movements from 1954 to 1962, which led to Algeria gaining its independence from France. An important decolonization war, it was a complex conflict characterized by guerrilla warfare, maquis fighting, terrorism against civilians, use of torture on both sides and counter-terrorism operations by the French Army. Effectively started by members of the National Liberation Front (FLN) on 1 November 1954 during the Toussaint Rouge ("Red All Saints' Day"), the conflict shook the French Fourth Republic's (1946–58) foundations and led to its collapse.

The war was a complex multi-faceted conflict which involved a large number of rival movements which fought against each other at different moments: On the independence side the FLN fought viciously against the Algerian National Movement (MNA) in Algeria and in the Café Wars on the French mainland; on the pro-French side, the French Army split during two attempted coups, while the right-wing Organisation de l'armée secrète (OAS) fought against both the FLN and the French government.

Under directives from Guy Mollet's SFIO government, the French Army initiated a campaign of "pacification" of what was considered at the time to be fully part of France. This "public order operation" quickly grew to a full-scale war. Algerians, who had at first largely favored a peaceful resolution, turned increasingly toward the goal of independence, supported by other Arab countries and, more generally, by worldwide opinion fueled by anti-colonialist ideas. Meanwhile, the French divided themselves on the issues of "French Algeria" (l'Algérie Française): whether to keep the status quo, negotiate a status intermediate between independence and complete integration in the French Republic, or allow complete independence. The French army finally obtained a military victory in the war, but the situation had changed and Algerian independence could no longer be forestalled.

Because of the instability of the French parliament, the French Fourth Republic was dissolved with Charles de Gaulle's return to power during the May 1958 crisis and his subsequent founding of the Fifth Republic and the establishment of a new Constitution constructed by himself and his Gaullist followers. De Gaulle's return to power was supposed to ensure Algeria's continued occupation and integration with the French Community, which had replaced the French Union and brought together France's colonies. However, de Gaulle progressively shifted in favor of Algerian independence, purportedly seeing it as inevitable. De Gaulle organized a vote for the Algerian people. The Algerians chose independence and France engaged in negotiations with the FLN, leading to the March 1962 Evian Accords which resulted in the independence of Algeria. After the failed April 1961 Algiers putsch organized by Generals hostile to the negotiations headed by Michel Debré's Gaullist government, the OAS (Organisation de l'armée secrète), which grouped various opponents of Algerian independence, initiated a campaign of bombings as well as peaceful strikes and demonstrations in Algeria in order to block the implementation of the Evian Accords and the exile of the pieds-noirs (Algerians of European origin). Ahmed Ben Bella, who had been arrested in 1956 along with other FLN leaders, became the first President of Algeria. To this day, the war has provided an important strategy frame for counter-insurgency thinkers, while the use of torture by the French Army has provoked a moral and political debate on the legitimacy and effectiveness of such methods. This debate is far from being settled as torture was used by both sides.

The Algerian war was a founding event in modern Algerian history. It left long-standing scars in both French and Algerian society, and still affects some segments of society in both countries to this day.[citation needed] After the 1997 legislative elections, won by the Socialist Party (PS), the National Assembly officially acknowledged in June 1999, 37 years after its end, that a "war" had taken place; while the Paris massacre of 1961 was recognized by the French state only in October 2001; on the other hand the Oran massacre of 1962 by the FLN has not been recognized yet by the Algerian state. Relations between France and Algeria are still deeply marked by this conflict and its aftermath.