This chapter discusses the consequences of linguistic diversity at the level of the individual, and the level of society, that is, the relationship of languages and their speakers within a given territory. It also considers the interaction of multilingualism and multiculturalism as two partially overlapping but non-identical concepts. Linguists tend to see multilingualism as a gradient phenomenon. Inter-Scandinavian communication is an example of what has been called receptive multilingualism with productive monolingualism. Haugen was one of the first linguists to draw attention to the fact that when Danes, Swedes, and Norwegians communicate with one another, they do not use a lingua franca. Many people become multilingual past childhood. Especially in the context of international migration and mobility, language acquisition continues for many throughout their lives. Australia is an example of a society which is characterized by extensive societal but not necessarily individual multilingualism.