The production of this book has been generously sponsored by the Stichting Bibliographie Linguistique, Leiden.This is an open access title distributed under the terms of the prevailing CC-BY-NC-ND License at the time of publication, which permits any non-commercial use, distribution, and reproduction in any medium, provided no alterations are made and the original author(s) and source are credited.Cover illustration: A group of young people using sign language in a discussion. Photo courtesy of Andries van Niekerk, National Institute for the Deaf, South Africa, http://www.nid.org.za. Andries van Niekerk is currently working on a Dictionary of South African Sign Language.