Although one-half of the Soviet Union's population is ethnically non-Russian, little attention is given them in Western demography. The present study deals with population changes in Estonia, primarily during the period since its annexation by the USSR. Although Estonia is not a typical Soviet Republic demographically, it is one of the more interesting ones. The paper focuses on three phenomena: immigration; urbanization; and differential ethnic growth. It is argued that immigration is the key to understanding population changes in Estonia, since it continually brings large numbers of Russians in the fertile age groups in to the country. Between 1950 and 1959 immigration was almost as large as natural increase, and since 1959 it has been larger. Most of the immigrants are regionally concentrated and urban. Due to continuous immigration of non-Estonians, their selective age structure, and their differing marriage and fertility patterns, the Estonians are steadily heading toward a minority status. In 1934 93% of the population was Estonian; in 1945 about 95%; in 1959 75%; in 1970 68%. However, this percentage varies across the age structure. Thus, in 1959 in the 70 and older age-group 91% were Estonian, while in the 0–9 group the figure was 67%.