This book provides explanations for the emergence of contact languages, especially pidgins and creoles. It assesses the current state of research and examines aspects of current theories and approaches that have excited much controversy and debate. The book answers questions such as: How valid is the notion of a pidgin-creole-postcreole life cycle? Why are many features of pidgins and creoles simple in formal terms compared to other languages? And what is the origin of the grammatical innovations in expanded pidgins and creoles - linguistic universals, conventional language change, the influence of features of languages in the contact environment, or a mix of two or more factors? In addressing these issues, the author looks at research on processes of second language acquisition and use, including simplification, overgeneralization, and language transfer. He shows how these processes can account for many of the characteristics of contact languages, and proposes linguistic and sociolinguistic constraints on their application in language contact. His analysis is supported with detailed examples and case studies from Pidgin Fijian, Melanesian Pidgin, Hawai'i Creole, New Caledonian Tayo and Australian Kriol, which he uses as well to assess the merits of competing theories of language genesis. Professor Siegel also considers his research's wider implications for linguistic theory.