As a result of German-Hungarian societal bilingualism German family names had been present in multilingual 19th century Hungary for centuries. Magyarizations of family names in the second half of the 19th century mostly affected the German and Yiddish speech communities bearing German family names. This paper explores the causes and characteristics of this phenomenon by examining the social, psychological, and ideological factors influencing the use of family names. After giving the numerical description of family name changes, the authors examine the sociolinguistic background of family name use, focusing on the situation of ethnolinguistic communities whose members bore German family names. By analysing the semantic structure of family names, the authors present how and why these family names could become tools of linguistic nationalism in contemporary Hungary, generating the claim of changing foreign-sounding family names to Hungarian ones. The political and social background of family name changes as well as social stratification of the applicants are also examined. The authors describe the movement of family name Magyarizations as a behavioural pattern of middle-class people ready to accept social mobility and willing to take part in assimilation. The aesthetic, functional and linguistic principles found behind these family name changes are also discussed. After briefly presenting the history of German family names in 20th century Hungary, the authors deduce some basic theoretical and methodological conclusions.