At the outset, the article highlights the development of Slovene sociolinguistics, dealing with languages in contact, to fo-cus on the contacts between the Slovene and the Italian languages in the ethnically mixed area of Slovene Istria. The second part offers an in-depth description of the ethnically mixed area of Slovene Istria, which in accordance with the Treaty of London, and later the Treaty of Osimo, introduced institutionalised bilingualism. However, numerous questions in relation to the level of communicative competence in the first and second languages of each individual and individual social groups remain open. The outcomes of the sociolinguistic research presented in the final part of the article confirm that communica-tive competence depends on a number of personal and social factors, and also on the so-called ethnic awareness, i.e. the at-titude of each individual to his own and co-existing culture as well as to intercultural values.