Korenizatsiia (Russian: коренизация, romanized: korenizatsiya, pronounced [kərʲɪnʲɪˈzatsɨjə]; transl. "indigenization" or "nativization") was an early policy of the Soviet Union for the integration of non-Russian nationalities into the governments of their specific Soviet republics. This term comes from the word korennoi in the phrase korennoi narod, which means "native people" or "indigenous population." In the 1920s, the policy promoted representatives of the titular nation, and their national minorities, into the lower administrative levels of the local government, bureaucracy, and nomenklatura of their Soviet republics. The main idea of the korenizatsiia was to grow communist cadres for every nationality. In Russian, the term korenizatsiya (коренизация) derives from korennoye naseleniye (коренное население, "native population"). The policy practically ended in the mid-1930s with the deportations of various nationalities.

Politically and culturally, the nativization policy aimed to eliminate Russian domination and culture in Soviet republics where ethnic Russians did not constitute a majority. This policy was implemented even in areas with large Russian-speaking populations; for instance, all children in Ukraine were taught in the Ukrainian language in school. The policies of korenizatsiia facilitated the Communist Party's establishment of the local languages in government and education, in publishing, in culture, and in public life. In that manner, the cadre of the local Communist Party were promoted to every level of government, and ethnic Russians working in said governments were required to learn the local language and culture of the given Soviet republic.

Lenin believed that nationalism had the potential to attract class allies for the Bolsheviks and that the historical distrust of non-Russian peoples toward Great Russians could be overcome in this way. Korenizatsiia was a preventive policy designed to stop the rise of nationalism among the non-Russian peoples who had been oppressed in the past. The Bolsheviks believed that Great Russian chauvinism was a bigger danger than local national movements. Because of this, korenizatsiia also included criticism of Russian culture and the use of the Russian alphabet, which were linked to the colonial and Russification policies of the former Tsarist regime. Korenizatsiia was also designed to support the decolonization process, which the Bolsheviks saw as unavoidable, while at the same time helping to maintain the territorial unity of the former Russian Empire.

The nationalities policy was formulated by the Bolshevik party in 1913, four years before they came to power in Russia. Vladimir Lenin sent a young Joseph Stalin (himself a Georgian and therefore an ethnic minority member) to Vienna, which was a very ethnically diverse city due to its status as capital of the Austro-Hungarian empire. Stalin reported back to Moscow with his ideas for the policy. It was summarized in Stalin's pamphlet (his first scholarly publication), Marxism and the National Question (1913).

The first clear and comprehensive expression of the policy was published by Joseph Stalin in an article in Pravda on October 10, 1920. In this article, Stalin stated that all Soviet institutions operating in the border regions—including courts, administration, economic bodies, local governments, and Party organizations—should be composed of individuals who understood the customs, way of life, and languages of the local populations. This statement marked a turning point in Soviet nationalities policy.

Korenizatsiia was later systematically defined, especially during the Party Congresses of March 1921 and April 1923, and was shaped around two main objectives:

As adopted in 1923 korenizatsiia involved teaching and administration in the language of the republic; and promoting non-Russians to positions of power in Republic administrations and the party, including for a time the creation of a special administrative units called natssovety (нацсоветы, national selsoviets) and natsrayony (нацрайоны, national districts) based on concentrations of minorities within what were minority republics. For example, in Ukraine in the late 1920s there were even natssovety for Russians and Estonians.^{[citation needed]}

In 1920s, there still was animosity towards the Russians and towards other nationalities on the part of the Russians, but there were also conflicts and rivalries among other nationalities.