This study presents an overview of the ethnic and demographic characteristics of Turkic indigenous peoples living in the Sayan-Altai region, including dynamics in marital structure, ethnically assortative marriage, and level of admixture among the Kumandins in the Altai Territory; the Shor in the Kemerovo Province; the Altai-Kizhi, Kumandins, Telengits, Tubalars, and Chelkans in the Altai Republic; and the Khakas (Kachin, Koibal, Kyzyl, and Sagai) in the Republic of Khakassia. Temporal and territorial differences in levels of interethnic mixing within the selected communities are revealed. The study shows that during the period 1940–2009, the rate of monoethnic marriages decreased and the number of interethnic marriages in virtually all communities under investigation increased with the exception of the southern Altaians and the Khakas-Sagai. Specifi c features of interethnic mixing are identifi ed. Marriage to representatives of the migrant (Russian-speaking) population prevails among the northern Altaians (Kumandins, Tubalars, and Chelkans), Khakas-Kyzyl, and Shor of the mountain taiga region, Kemerovo Province. Marriages to members of other indigenous peoples in southern Siberia are common among the Khakas-Koibal, Khakas-Kachin, and the Abakan Shor. These trends illustrate the nature of ethnic and demographic development in the Sayan-Altai region.