Martin J. Ball is Professor of Speech Language Pathology at Linköping University, Sweden. He is co-editor of the journal Clinical Linguistics and Phonetics (Taylor & Francis), and the book series Communication Disorders Across Languages (Multilingual Matters). His main research interests include sociolinguistics, clinical phonetics and phonology, and the Celtic languages. David Crystal is Honorary Professor of Linguistics at the University of Bangor, UK. Since 1984, he has worked from his home in Holyhead, North Wales as a writer, editor, lecturer and broadcaster on linguistics, applied linguistics, and English language studies. His books include The Cambridge Encyclopedia of Language (2010), The Stories of English (2005) and Internet Linguistics (2011). Paul Fletcher is Emeritus Professor of Speech and Hearing Sciences at University College Cork, Ireland. Since the 1970s he has published widely on language development and language impairment in children speaking English, and more recently on those speaking Cantonese and Mandarin. His research focus, initially primarily on syntax, has broadened to include vocabulary, and the interaction between vocabulary and syntax in language development.