The paper describes the phenomenon of Karelian-Russian everyday bilingualism as a significant component of the language/speech polylingualism problem. The transformation of its objective and major subjective factors and traits over the 20th–21st centuries is revealed through analysis of the language- and ethno-confessional identity, evaluation and status of the native and the Russian languages, speech as a component of social communication of specific local groups of Tver Karelians. The interpretation of published, archival and the author’s own field materials, collected over a period of 30 years – from the 1980s to 2012, was undertaken in a historical projection using the methodological techniques of ethnology, ethno-linguistics, linguistic culturology and sociolinguistics.