The AB-Aktion (German: Außerordentliche Befriedungsaktion lit. 'Extraordinary Pacification Operation', Polish: Akcja AB) was the second stage of the Nazi German campaign of violence in Poland early in World War II, taking place between March and September 1940. As with the previous Intelligenzaktion, during the 1939 invasion of Poland, it aimed to eliminate the intellectuals and the upper classes of the Second Polish Republic. While the Intelligenzaktion had taken place in the territories of western Poland annexed by Germany, perpetrated by Einsatzgruppen following closely behind the German Army, AB took place in the General Government (GG), the territories that were merely occupied and remained nominally part of Poland. Both primarily targeted present and former government officials, social and political activists, artists, educators, local business leaders and priests, all of whom the Germans believed would be instrumental in leading resistance to their rule, regardless of whether those targeted were actually inclined to do so. With the intellectuals eliminated, the Germans believed the remaining Polish population would be docile and useful to them as unskilled labour while they completed their plans to Germanize Poland and extirpate Polish cultural, ethnic and national identity.

The November 1939 Sonderaktion Krakau, in which 150 faculty and staff at Jagiellonian University in Kraków were arrested and sent to concentration camps on the initiative of the local SS chief Bruno Müller, became a template for the AB Aktion. Most of those arrested then survived their time in the camps and were released within months, following pressure from the Vatican and the Italian government. Adolf Hitler had personally charged Hans Frank, the German General Governor, with keeping Poland stable to avoid distractions the invasion of France the following year. Frank concluded that it would be better to execute those arrested shortly afterwards, to avoid the same pressure, when the security apparatus made their next wave of arrests before the France campaign.

In spring 1940 Frank, the four district governors and the corresponding security and military officials held several conferences, including some jointly with the Soviet NKVD, to formalize the plans for AB. Shortly afterwards the Gestapo, SS, SD and SiPo in the GG began arrests. Over 30,000 Polish citizens were taken into custody over the next several months. It is believed that about 7,000, including those labeled as suspected of criminal activities), were subsequently massacred secretly at various locations, such as the forest complex near Palmiry northwest of Warsaw. Despite Frank's initial intentions to quickly execute all those arrested, at Reichsfüherer Heinrich Himmler's request many were sent to concentration camps where they often died, including the first group of prisoners to arrive at Auschwitz. Memorials to the victims of AB have been erected in many of the places, usually in remote forests, where they were taken to be shot.

The resistance soon recovered from the major setback AB inflicted. By late 1941 the German authorities decided to instead use tactics that more specifically targeted known or suspected underground groups, as more Poles from all walks of life began taking action against the occupiers, contrary to German expectations. Mass executions did continue as a method of state terror, joined later by the extermination of Jews, Roma and others the Nazis considered racially undesirable. After the war, some of those responsible, such as Frank, were executed for war crimes, while others involved at lower levels either died before they could be tried on the charges they faced, or evaded prosecution by living under assumed names.

The Nazis considered the Polish intelligentsia to include not just the country's academics and artists, but its politicians, artists, aristocrats, professionals, clergy, present and former military officers, and generally everyone sufficiently educated or wealthy to have a position of authority, even informally, in Polish society. Their ideology held that only these people had a true national consciousness; the rest of the population was indifferent to the fate of the state and cared more about their daily lives. Once the intelligentsia had been eliminated, the Nazis believed the remaining Poles would be useful to them as unskilled labour.

The first mass murder of the intelligentsia, and any other people suspected of potential anti-Nazi activity, began in September 1939 as German troops began invading Poland and continued until the next spring. This was seen by Nazi Germany as a pre-emptive measure to keep the Polish resistance scattered and to prevent the Poles from revolting during the planned German invasion of France.

This was the Intelligenzaktion, a plan to eliminate Poland's intelligentsia and leadership in the western and central part of the present Polish state, territory annexed by Germany after the invasion, realized by Einsatzgruppen and Volksdeutscher Selbstschutz, a militia raised from the ethnic Germans in Poland. As the result of this operation 100,000 Polish nobles, teachers, entrepreneurs, social workers, priests, judges and political activists were arrested (save those whose skills were temporarily needed for civil administrative purposes) in 10 regional actions. Of those, nearly 50,000 were executed and the rest sent to concentration camps that few survived.

The Intelligenzaktion was also extended to the General Government (GG), the German-occupied rump of Poland not annexed to either the Soviet Union or Germany after the invasion. In general those actions were less intense and less lethal, sparing most of the Catholic clergy and larger landowners. One such action, the November 1939 Sonderaktion Krakau, in which the president and the entire faculty Jagiellonian University in Kraków were arrested and sent to concentration camps, drew condemnation from Fascist Italy and the Vatican. All those who had survived their incarceration were eventually released; some died shortly afterwards as a result of maltreatment and undernourishment in the camps.