David Crystal is Honorary Professor of Linguistics at the University of Bangor, formerly at the University of Reading, and a Fellow of the British Academy. He has been author, co-author, or editor of over 120 books, including several benchmark reference volumes such as The Cambridge Encyclopedia of Language (1987, 1997, 2010) and The New Penguin Encyclopedia (2003), and books that have spread awareness of linguistics to general readers, such as The Stories of English (2004).Alan C. L. Yu is the William Colvin Professor of Linguistics and the College at the University of Chicago. His research focuses on language variation and change, particularly from an individual-difference perspective. He is the author of A Natural History of Infixation (2007), the editor of Origins of Sound Change: Approaches to Phonologization (2013), and co-editor of The Handbook of Phonological Theory, Second Edition (2011, Wiley Blackwell). He is co-General Editor of Laboratory Phonology and Associate Editor of the International Journal of American Linguistics.