In this chapter we will consider the various ways in which different languages, as opposed to mere geographical or social varieties of the same language, may be affected by mutual contact. Although all transfer of language material across language boundaries may be said to be the result of some measure of bilingualism on the part of those who do the conveying, the precise nature and extent of the linguistic exchange will depend upon the detailed circumstances of the social and cultural relations between the communities concerned. In the following pages the notion of ‘contact’ will be interpreted in a very wide sense, so as to include not only close geographical proximity but also trade relations and other types of cultural encounter of varying degrees of sophistication. The most superficial kind of language contact is probably that which exists between the producers or conveyors of some commodity and their clients in other language areas, and it is a well-documented fact of recent language history that the names of such objects of international trade as tea, coffee, or tobacco readily travel with them and become part of the consumers' language. At the other end of the scale the most intensive kind of contact may be said to exist in fully bilingual communities, and here not merely lexical items but even phonological and grammatical rules may come to be shared by the languages in question.