Languages are said to come into contact when their speakers interact with one another. The linguistic and sociolinguistic consequences of long-term contact between languages arc studied in the subfield of linguistics called 'contact linguistics'. Two of the major concerns of contact linguistics are contact-induced language change and the formation of new contact varieties such as new dialects, pidgins and creoles. However, the actual site of language contact is in the minds of individuals using more than one language (Weinreich (1970) [1953]). Thus, second language acquisition (SLA), an individual psycholinguistic process involving two languages is by definition a kind of language contact. Changes that occur in languages, or the new varieties that emerge, must have originated in individuals' ways of speaking. This chapter examines the role of processes of SLA in individuals that may ultimately lead to the outcomes of language change or the emergence of new contact varieties in communities of speakers.