The 1973 Chilean coup d'état was a military coup in Chile that deposed the Popular Unity government of President Salvador Allende. On 11 September 1973, after an extended period of social unrest and political tension between the opposition-controlled Congress and the socialist President, as well as economic war ordered by U.S. President Richard Nixon, a group of military officers led by General Augusto Pinochet seized power in a coup, ending civilian rule.

The military established a junta that suspended all political activity in Chile and repressed left-wing movements, especially communist and socialist parties and the Revolutionary Left Movement (MIR). Pinochet rose to supreme power within a year of the coup and was formally declared President of Chile in late 1974. The Nixon administration, which had worked to create the conditions for the coup, promptly recognized the junta government and supported it in consolidating power.During the air raids and ground attacks that preceded the coup, Allende gave his final speech, vowing to stay in the presidential palace and refusing offers of safe passage should he choose exile over confrontation. Direct witness accounts of Allende's death agree that he killed himself in the palace.Before the coup, Chile had been hailed as a beacon of democracy and political stability for decades, a period in which the rest of South America had been plagued by military juntas and caudillismo. The collapse of Chilean democracy ended a succession of democratic governments in Chile, which had held democratic elections since 1932. Historian Peter Winn characterised the 1973 coup as one of the most violent events in the history of Chile. A weak insurgent movement against the Pinochet regime was maintained inside Chile by elements sympathetic to the former Allende government. An internationally supported plebiscite in 1988 held under the auspices of the military dictatorship was followed by a peaceful transition to an elected civilian government.

Due to occurring on the same date as the September 11 attacks in 2001, the coup has often been referred to as "the other 9/11".