The Organisation de l'armée secrète (OAS; Secret Army Organization) was a short-lived French right-wing terrorist group formed in February 1961 to resist the granting of independence to the French colony of Algeria (Algérie française).

The OAS was created in response to the referendums on self-determination for Algeria. There were uprisings in January 1960 by the colons and pieds noirs who again took to arms in April 1961 (the Generals' Putsch). Both these insurrections were swiftly suppressed and many of the leaders who had created the OAS were imprisoned. By terrorist acts and assassinations (Mouloud Feraoun) they, like the Front de libération nationale (FLN), attempted to alter the events of the Algerian War. Both groups were considered terrorist organizations trying to encourage change.

The OAS attempted to assassinate president Charles de Gaulle several times. The most prominent attempt was a 1962 ambush at Petit-Clamart, a Paris suburb, planned by military engineer Jean-Marie Bastien-Thiry.

The main hope of the OAS was to provoke the FLN into restarting military action after a cease-fire was agreed in the Evian Accords of March and the referendum of June 1962; over 100 bombs a day were detonated by the OAS in March. Despite the carnage the FLN remained resolute and on June 17, 1962 the OAS agreed to the ceasefire. In April 1962 its leader, Raoul Salan was captured. The group was effectively eliminated by 1963. However the group was granted an amnesty for its actions and few members were properly tried or significantly imprisoned, though some, including ringleader Bastien-Thiry, were executed by firing squad.

An assassin hired by the OAS is the principal villain in Frederick Forsyth's (fictional) novel, The Day of the Jackal.