The National Reorganization Process (Spanish: Proceso de Reorganización Nacional, PRN; often simply el Proceso, "the Process") was the military dictatorship that ruled Argentina from the coup d'état of March 24, 1976, until the unconditional transfer of power to a government elected by the citizens on December 10, 1983. In Argentina it is often known simply as the última junta militar ("last military junta"), última dictadura militar ("last military dictatorship"), última dictadura cívico-militar ("last civil–military dictatorship"), or última dictadura cívico-eclesial-militar ("last civil–clerical-military dictatorship") — because there have been several in the country's history and no others like it since it ended. It took the form of a bureaucratic-authoritarian state and was characterized by establishing a systematic plan of state terrorism, which included murders, kidnappings, torture, forced disappearances, and the kidnapping of babies (and concealment of their identity). It is considered "the bloodiest dictatorship in Argentine history".

The Argentine Armed Forces seized political power during the March 1976 coup against the presidency of Isabel Perón, the successor and widow of former President Juan Perón, at a time of growing economic and political instability. Congress was suspended, political parties were banned, civil rights were limited, and free market and deregulation policies were introduced. The President of Argentina and his ministers were appointed from military personnel while leftists and Peronists were persecuted. The junta launched the Dirty War, a campaign of state terrorism against opponents involving torture, extrajudicial murder and systematic forced disappearances. Public opposition due to civil rights abuses and inability to solve the worsening economic crisis in Argentina caused the junta to invade the Falkland Islands in April 1982. After starting and then losing the Falklands War against the United Kingdom in June, the junta began to collapse and finally relinquished power in 1983 with the election of President Raúl Alfonsín.

Members of the National Reorganization Process were prosecuted in the Trial of the Juntas in 1985, receiving sentences ranging from life imprisonment to courts-martial for mishandling the Falklands War. They were pardoned by President Carlos Menem in 1989 but were re-arrested on new charges in the early 2000s. Almost all of the surviving junta members are currently serving sentences for crimes against humanity and genocide. Some scholars describe the regime as being characteristic of neo-fascism.

The military of Argentina has always been highly influential in Argentine politics, and Argentine history is laced with frequent and prolonged intervals of military rule. The popular Argentine leader Juan Perón, three-time President of Argentina, was a colonel in the army who first came to political power in the aftermath of a 1943 military coup. He advocated a new policy dubbed Justicialism, a nationalist policy that he claimed was a "Third Position", an alternative to both capitalism and communism. After being reelected president by popular vote, Perón was deposed and exiled by the Revolución Libertadora in 1955.

After a series of weak governments and a seven-year military government, Perón returned to Argentina in 1973 after 18 years in exile in Francoist Spain, amid escalating political unrest, divisions in the Peronist movement, and frequent outbreaks of political violence. His return was marked by the 20 June 1973 Ezeiza massacre, after which the right wing of the Peronist movement became dominant.

Perón was democratically elected president in 1973, but died in July 1974. His vice president and third wife, Isabel Perón, succeeded him, but she proved to be a weak, ineffectual ruler. A number of revolutionary organizations—chief among them Montoneros, a group of far-left Peronists—escalated their wave of political violence (including kidnappings and bombings) against the campaign of harsh repressive and retaliatory measures enforced by the military and the police. In addition, right-wing paramilitary groups entered the cycle of violence, such as the Triple A death squad, founded by José López Rega, Perón's Minister of Social Welfare and a member of the P2 masonic lodge. The situation escalated until Mrs. Perón was overthrown. She was replaced on 24 March 1976 by a military junta led by Lieutenant General Jorge Rafael Videla.

Official investigations undertaken after the end of the Dirty War by the National Commission on the Disappearance of Persons documented 8,961 desaparecidos (victims of forced disappearance) and other human rights violations, noting that the correct number must be higher. Many cases were never reported, when whole families disappeared, and the military destroyed many of its records months before the return of democracy. Among the "disappeared" were pregnant women, who were kept alive until giving birth under often primitive circumstances in the secret prisons. The infants were generally illegally adopted by military or political families affiliated with the administration, and the mothers were generally killed. Thousands of detainees were drugged, loaded into aircraft, stripped naked and then thrown into the Rio de la Plata or the Atlantic Ocean to drown in what became known as "death flights".

The film The Official Story (1984), which won the Oscar for the Best Foreign Language Film category in 1985, addresses this situation. The Argentine secret service SIDE (Secretaría de Inteligencia del Estado) also cooperated with the DINA in Pinochet's Chile and other South American intelligence agencies. Eight South American nations supported endeavours to eradicate left-leaning groups on the continent, known as Operation Condor, a United States-backed campaign of anti-democratic and political repression and state terror. It is estimated to have caused the deaths of more than 60,000 people. SIDE also trained—for example in the Honduran Lepaterique base—the Nicaraguan Contras who were fighting the Sandinista government there.