The article focuses on structural changes in the Bratislava population in the first half of the 20th century. Particularly in the decade of 1939–1948, there was an intense social engineering, i.e. a targeted effort to adjust both the ethnic and social city structures to the contemporary regime needs. The Czechs were the first target of these efforts (1939), followed by the Jewish minority (deportations in 1942); after the liberation, both Hungarian and German inhabitants fell victims to such activities, and after February 1948, this process also affected some social strata of the population. (A mass emigration after August 1968 was due to different reasons.) When analyzing the social engineering, the author has used particularly memories of the contemporary witnesses supported by the archive and other sources.