This chapter depicts major theories of language contact, including those relating to the outcomes of borrowing, creole formation and other bilingual mixtures, with special emphasis on the framework proposed by Frans van Coetsem. This framework is multi-disciplinary in nature, built around linguistic, sociolinguistic, and psycholinguistic approaches. I first discuss the contributions of sociolinguistic approaches to our understanding of the ways in which social contexts and social factors influence the outcomes of language contact. I then evaluate various linguistic frameworks that have been proposed for describing the linguistic outcomes of language contact, the mechanisms involved, and the classification of contact phenomena. I argue that van Coetsem’s (1988, 2000) model of language contact offers a more consistent, accurate and principled explanation of the processes of change associated with different types of contact. Following that, I show how a wide variety of contact phenomena can be accounted for in terms of just two universal mechanisms of change—borrowing and imposition. Finally, I discuss ways in which psycholinguistic models of language production can contribute to our understanding of these mechanisms of contact-induced change.