Double genocide theory (Lithuanian: Dvigubo genocido požiūris, lit. 'Double genocide approach') is a term used to refer to the claim that the atrocities committed by the Soviet Union against Eastern Europeans constitute a genocide that was equivalent in scale and nature to the Holocaust, in which approximately six million Jews were systematically murdered by Nazi Germany. The theory first gained popularity in Lithuania after the fall of the Soviet Union in 1991, particularly in discussions about the Holocaust in Lithuania.

A more extreme version of the theory vindicates the actions of local Nazi collaborators as retaliatory by accusing Jews of complicity in Soviet repression, especially in Lithuania, eastern Poland, and northern Romania. Scholars have criticized the double genocide theory as a form of Holocaust trivialization.

After the fall of the Soviet Union, many post-Soviet states, particularly the Baltic states, built more memorials to victims of the Soviet occupation, and devoted public resources to historical committees that prioritized their nations' suffering under Soviet occupation over the suffering of their nation's Jews under Nazi occupation.

In Lithuania, the Museum of Genocide Victims (now the Museum of Occupations and Freedom Fights) was opened in 1992, memorializing the victims of crimes against humanity during Soviet occupation, but rarely mentioned the Holocaust in Lithuania. Until 2011, the Holocaust was mentioned only once in the entire museum, compared to the two rooms devoted to the Soviet occupation. According to Ljiljana Radonić, a political scientist specializing in national memory, said that "the way in which Jewish victims are portrayed there shows that this reference to the Holocaust is merely perfunctory." In Lithuania's state Jewish museum's main building, a plaque asserts that "The first killings of Jews have been performed in the context of the war chaos." In this context, some basic postulates of the double genocide theory were developed. Some Lithuanian nationalists, backed by the state, claimed that various nationalist collaborators were anti-Soviet heroes, that Jewish victims were merely collateral damage in the fog of war, and any documentation that counters this is Soviet propaganda. However, the historical record shows that Lithuanian Jews were targeted for extermination—based on their ethnicity—by both the Nazis and local nationalist forces, with local nationalists taking a leading role in the genocide.

Lithuanian historian Vytautas Berenis commented that the double genocide theory has considerable influence in Lithuanian historiography and journalism. Berenis states that Lithuanian nationalists excuse their country's collaboration by asserting that collaborators were merely retaliating against "Jewish communists" that were allegedly over-represented in the ranks of the NKVD and communist party cadres. Berenis says that this theory is incorrect on the merits. Many Jews did not support the Soviets—a disproportionate number of Jews were victims of Soviet deportations. Further, in October 1940, 68.49 percent of members of the Lithuanian Communist Party were ethnic Lithuanians, while 16.24 percent were Jews—but nearly all the victims of nationalist atrocities were Jews. Poet and dissident Tomas Venclova criticized the concept of double genocide in his 1975 essay "Žydai ir lietuviai" ("Jews and Lithuanians") and subsequent publications. According to Venclova, the theory obscures the role of Lithuanians in crimes against humanity committed in Lithuania by assigning all guilt to non-Lithuanian actors.

According to the "Jews in Latvia" Museum director Ilja Lenskis, Jews similarly made up about 12% of the deportees in June deportation from Latvia, while being only 5% of the general population, therefore the narrative that Latvian Jews were "avid supporters of the Soviet regime is simply false, but was a narrative extensively spread by Nazi propaganda" as "the Nazis, who occupied Latvia a bit more than a week after the June Deportations, exploited this trauma" and "offered the very simple explanation that the Jews are guilty".

In 2010, political scientist Evgeny Finkel commented: "There is hardly any country in the vast region from Estonia in the north to Kazakhstan in the south in which either the authorities or the opposition have not seriously considered the idea of officially recognising past sufferings as genocides, often finding creative ways to reconcile the legal definition of the concept ... and the historical record."

According to Michael Shafir, the double genocide theory is at worst Holocaust obfuscation. Political scientist Clemens Heni [de] sees it as a form of Holocaust trivialization. Historian Alexander Karn writes that the idea of double genocide "hinge[s] upon the erasure of Lithuanian participation in the Holocaust". Ethnologist Carole Lemée sees it as a symptom of persistent antisemitism.