This book brings together what has been learned about the relationships between human languages, cognition, and the brain through reviewing studies of signed languages and their Deaf users. The text claims to be written for the general reader, although there is much to recommend it for the more specific or advanced reader interested in the development, use, and insights from sign language research. The author first attempts to ‘‘debunk’’ a number of common myths about sign languages and to inform the reader about the issues, terminology, and sign coding conventions that are to be encountered in successive chapters. The author then traces the emergence of sign languages as human language and focuses on the characteristics of developed and relatively well-documented sign languages (for example, American Sign Language), as well as an emerging sign language (Nicaraguan Sign Language).