Our collaboration on this book began, fittingly, in the Basque country, when we were invited to talk about trilingualism. It is probably not accidental that this meeting should have encouraged us to embark on a project about multilingualism: we found ourselves in a bilingual country, were giving our papers in a third language, English, and we were drawing on our experiences of multilingual family environments.

For over half a century now, ‘bilingualism’ (the use of two languages) has become the subject of systematic scholarly investigation. Bilingualism has been scientifically reported on as an alternative to (sometimes as a divergence from) monolingualism. In this sense, the study of bilingualism encompassed any language situation in individuals or societies that involved more than one language. Mostly it covered contact situations between two languages but it also subsumed other contexts involving trilingualism or multilingualism. In this book we propose to look at ‘trilingualism’ (the use of three languages) and multilingualism (the use of more than two languages) as distinct from bilingualism because we feel that the subject merits separate treatment, both when looking at individuals who acquire and use three (or more) languages and when taking a wider sociolinguistic perspective. Naturally, it is not always possible to draw a clear line between the number of languages present in certain contact situations, especially in sociolinguistic contexts, and our use of the term multilingualism takes cognisance of that.