This book presents a technology to help speech-, hearing- and sight-impaired people. It explains how they will benefit from an enhancement in their ability to recognize and produce speech or to detect sounds in their surroundings. Additionally, it is considered how sound-based assistive technology might be applied to the areas of speech recognition, speech synthesis, environmental recognition, virtual reality and robots. The primary focus of this book is to provide an understanding of both the methodology and basic concepts of assistive technology rather than listing the variety of assistive devices developed. This book presents a number of different topics which are sufficiently independent from one another that the reader may begin at any chapter without lacking background information. Much of the research quoted in this book was conducted in the author's laboratories at Hokkaido University and University of Tokyo. This book offers the reader a better understanding of a number ofunsolved problems that still persist in the field of sound-based assistive technology.