The enormous interest code-switching and related practices have found in linguistics over the last three decades is at least in part (i.e. in addition to internal developments in linguistics) due to the demise of the monolingual national language ideologies which have become less and less realistic in the age of globalization, transnationalism, and migration. Today, multilingual practices are an undisputed everyday phenomenon, even in the European nation states which hitherto considered themselves to be monolingual (see Stroud 2007 for a view beyond Europe). As with most other linguistic activities, code-switching can be seen from a number of different angles. Code-switching is the most striking surface manifestation of bilingualism and as such can be investigated from the point of view of speech production; it can be seen as a particularly interesting outcome of language contact in grammar; it can be treated as (part of) a sociolinguistic style which has identity-related functions; it can be investigated in the context of bilingual first language acquisition; it may be a sign of (imminent) structural convergence between two languages, or a sign of language attrition; and it may be treated as a linguistic activity or practice in its own right. In the following sections, the article discusses some terminological and methodological issues, followed by a brief historical overview of the genesis of the field of code-switching studies. Next, it addresses in greater detail the social and interactional meaning of code-switching as it emerges from sociolinguistic studies and how it can be analyzed in interactional (conversation-based) terms. The following section is devoted to grammatical constraints on code-switching. By way of conclusion, it suggests a number of areas for future research: code-mixing and -switching in small children; bilingual interactions among older children and in a community setting; acquisition in young and very young children in immigrant and lower class contexts; code-switching in the classroom etc. Another burgeoning area is psycholinguistic studies on the production and perception of code-mixing. Finally, there is the big but unresolved question of whether and how switching and mixing contribute to language change.