Language contact occurs when speakers of different languages interact and their languages influence one another. Drawing on the author's own first-hand observations of child and adult bilingualism, this book combines his original research with an up-to-date introduction to key concepts, to provide a holistic, original theory of contact linguistics. Going beyond a descriptive outline of contact phenomena, it introduces a theory of contact-induced language change, linking structural change to motivations in discourse and language processing. Since the first edition was published, the field has rapidly grown, and this fully revised edition covers all of the most recent developments, making it an invaluable resource for researchers and advanced students in linguistics.