The Katyn massacre was a mass execution of Polish officers and citizens ordered by the Soviet authorities in 1940 in a forest near Katyn, west of Smolensk in Russia in April 1940. The massacre was a carefully planned attempt to liquidate the Polish society's elite and thus impede the restoration of an independent Polish state after the Soviet Union and Germany had occupied Polen in 1939.

 In 1943 found the Germans the mass graves near Katyn. There were approx. 4000 officers. The revelation led to a rift between the USSR and the Polish government in exile in London and stressed the relationship between the USSR and Poland after the war when it was taboo to mention the massacre in the two countries.

 When the Soviet Union in 1943 denied the International Red Cross to conduct a study to clarify the responsibility for the crime, the Germans did it themselves. The Danish forensic Helge Tramsen was one of the 12 non-German doctors, which the Germans in April 1943 sent out to examine the corpses. They held the time of death to be spring 1940, when the Katyn area was occupied by Soviet troops.

 At the Nuremberg Trials refused the Western Allied judges to accept the Soviet demand that Germany was convicted of the crime. Right up to 1990 the Soviet government claimed that it was the Germans who had carried out the mass assassination, but then it was officially acknowledged that Joseph Stalin bore the responsibility. In 1992 gave the Russian president Boris Yeltsin, his Polish counterpart Lech Walesa a copy of a classified document on which the massacre is mentioned, it was dated 5th March 1940 and signed by L. Berija. The document was countersigned by Stalin, Vyacheslav Molotov, Kliment Voroshilov and Anastas Mikoyan, and approved by Mikahil Kalinin and Lazar Kaganovitj.

In 1989-1990 was more similar graves uncovered elsewhere in Russia. Most of the other Polish officers were murdered in the village near the city of Tver Mednoje (6100) and in Piatikhatki in the city outskirts of Kharkov (4000). The remaining is spread in small groups all over Russia. In all, 25,700 Poles have been executed, but according to Soviet data, the final numbers were 21,857.

One of the victims was the Polish film director Andrzej Wajdas father Jakub Wajda, who was executed in the NKVD prison in Kharkov in the spring of the 1940th. His father's death led to the Wajdas Oscar-nominated film from 2007 about the massacres titled Katyn.