An essential handbook for professionals and advanced students in the field. Volume 1 contains comprehensive studies on the acquisition of 15 different languages (from ASL to Samoan) — written by top researchers on each topic. Volume 2 concentrates on theoretical issues, emphasizing current linguistic and psycholinguistic research. Unique in its approach toward individual languages and in its comparative perspective, this book is a hallmark of a rapidly growing area of interdisciplinary, international research.