The monograph, based on broad studies into the Polish diaspora in Sweden, provides a picture of the social factors influencing the maintenance of the heritage language and culture by the second generation of emigrants. The author’s main objective, however, is to discover the systemic mechanisms underlying language acquisition by children in a bilingual setting and to investigate the influence of the interference from the dominant language on the acquisition of Polish. A particular attention is devoted to the category of case, which is absent from Swedish. Although it, generally, represents a description of a particular linguistic material, in fact the book addresses problems of the theory of language acquisition. The results and conclusions enable a better understanding of the universal semiotic and psychological principles that motivate the structure of the grammatical system of a natural language.