Societal multilingualism comes about in a number of ways, virtually all of them a result of cross-cultural contact and social necessity. It can have a long-term existence where – for example – political union has brought different language communities under one roof. It can be less permanent in others, as in situations where patterns of migration and assimilation lead, over time, to language erosion. Multilingualism can also reflect the simultaneous existence of varieties of greater and lesser prestige. It can have a simple de facto status, or it may reflect official or legislated policies at state or regional levels. Relatedly, multilingualism may arise “naturally” and without explicit instruction, or it may be a product of more formal educational undertakings. Multilingual capabilities may exist for instrumental communicative reasons, or they may be sustained through powerful symbolic language-and-identity associations, or both. When languages come into contact with one another, it is common to find that some are more dominant than others – in some or perhaps all social spheres – and this situation often leads to efforts towards the maintenance or even rejuvenation of weaker varieties. language and assimilation, language and conflict, language and contact, language and identity, language and instrumentality, language maintenance, language and migration, language and prescriptivism, language and prestige, language revival, language and status, language and symbolism