The article is a sociolinguistic study of the long-standing German-speaking Lutheran minorities in two adjacent provinces of the 19th-century Russian Empire ('Mazowsze', in present-day Poland, and 'Suwalszczyzna', in present-day southwestern Lithuania). Based on archival and field research, the study examines how members of this ethnoconfessional minority and their descendants perceived their own language, cultural, and ethnic identity over the 200+ years that they lived, as Russian citizens, in a community with multiple dominant languages (Polish, Russian, and sometimes Lithuanian). The study focuses on the Lutheran settlers and their descendants, who tended not to lose the language as quickly as their Roman Catholic counterparts, as the Lutheran liturgy, Sunday School lessons, and Confirmation training all required an ability to read and speak German. There are indications, however, that the cultural and language self-identification of the Lutheran Russian Germans was more complex than the historical scenario suggests. The most striking factor is their multilingualism: by the mid-19th century, most Russian Germans were native-level speakers of Polish, and many were trilingual in Lithuanian. Many had at least an elementary knowledge of Yiddish, and after 1868, when Russian replaced Polish as the state language, those who went to school learned to read and write in Russian. Comparing data from both before and after 1868 on language choice, language interference between Russian and Polish, and individual naming and signature practices, the article draws the conclusion that most German-speaking Lutherans in Mazowsze and Suwalszczyzna identified themselves linguistically and culturally not only with German, but also, to a significant extent, with Polish and, to a lesser extent, with Russian.