The primary aim of this paper is to make explicit and to analyse linguistics norms and interactional competence of bilinguals and the innovative and creative aspects of interferences in their speech. It attempts to explore these phenomena on the basis of data from the longitudinal sociolinguistic project among bilingual Estonians and Germans in Australa, the USA, Canada and Sweden. The main objective of this project, which started in 1967, is an examination of the linguistic norms and the variable competence of bilinguals and the construction of explicit models of bilingual behaviour. From this base its purpose is to contribute to a theory of code switching and interference and to illustrate special relations between the bilingual's languages and his socio-cultural environment. Language maintenance, language innovation and language shift problems are analysed against the background of the bilingual's social status.