The book describes one of the most characteristic phenomena accompanying bilingualism – the change of language within a communication situation on the material of a particular community: the Polish language island in Siberia, the village of Vershina in the Irkutsk Oblast, founded in 1910 by voluntary settlers from Lesser Poland. The collection of rich field material allowed for a comprehensive analysis of the social and cultural determinants of code-switching and code-mixing in the conditions of contact between the Lesser Poland dialect and the Russian language in group and individual dimensions.