Widespread multilingualism is one form of language contact. Multilingualism was more common in the past than is usually supposed: in early times, when most people were members of small language communities, it was necessary to know two or more languages for trade or any other dealings outside one's own town or village, and this holds good today in places of high linguistic diversity such as Sub-Saharan Africa and India. Linguist Ekkehard Wolff estimates that 50% of the population of Africa is multilingual.

In multilingual societies, not all speakers need to be multilingual. Some states can have multilingual policies and recognise several official languages, such as Canada (English and French). In some states, particular languages may be associated with particular regions in the state (e.g., Canada) or with particular ethnicities (Singapore). When all speakers are multilingual, linguists classify the community according to the functional distribution of the languages involved:

Multilingualism within communities
Learning language
Sequential model
Definition of multilingualism