This book systematically discusses the link between bilingual language production and its manifestation in historical documents, drawing together two branches of linguistics which have much in common but are traditionally dealt with separately. By combining the study of historical mixed texts with the principles of modern code-switching and bilingualism research, the author argues that the cognitive processes underpinning the human capacity to produce mixed utterances have remained unchanged throughout history, even as the languages themselves are constantly changing. This book will be of interest to scholars of historical linguistics, syntactic theory (particularly generative grammar), language variation and change.