Manual signs are used worldwide to support the communication and language development of children who have developmental disabilities. This book provides an overview of forty years of research and practice by recognised experts, from a developmental perspective. Uniquely, the book includes contributions on both sign languages and sign systems, linking the two fields of Deaf studies and Augmentative and Alternative Communication which have historically been seen as separate. This text is the most authoritative single text to date on the topic, providing an invaluable resource for speech pathologists, researchers, psychologists and educators. The main sections of the book include: the typical development of sign language and of gesture; literature reviews on sign acquisition in children with disabilities such as Down syndrome, autism spectrum disorders, Llandau Kleffner syndrome and deaf blindness. An important chapter deals with the latest research on sign language impairments in deaf children with developmental language difficulties, or autism spectrum disorders. The third section of the book addresses assessment and intervention, covering vocabulary, sign production difficulties and intelligibility, grammar and multi-signing, and pragmatics and discourse skills. The final two sections are concerned with use of signs in context: in the home, in school, and in different cultures. Throughout, care is taken to ensure that the voices of users are present and vivid, whether these be family members, teaching staff or the children themselves, with an entire chapter given over to an interview with a young adult's reflections on her use of sign since childhood. The book concludes with a call for a multimodal perspective on augmentative communication to be adopted in the future.