This article discusses the changing ethnic composition of the Soviet population as a whole and by region. It examines the proximate demographic sources of change for different regions of the country, with special emphasis on fertility and migration. It shows that differences in population growth rates during the last 30 years have led to marked changes in the ethnic composition of the USSR and that such changes will continue in the future. The analysis focuses on the population of the USSR and that such changes will continue in the future. The analysis focuses on the population of the USSR as a whole as well as of the 15 union republics that comprise the federal state structure. The titular nationalities of these republics — the nationalities for which the republics are named — comprise 90.3 percent of the population of the Soviet Union in 1989.