Although speech is the most natural form of communication between humans, using speech to communicate with machines is anything but natural. Drawing from psychology, human-computer interaction, linguistics, and communication theory, this book provides a comprehensive yet concise survey of practical speech user interface design. The text presents research and practice-based guidance for the development of usable speech user interfaces, such as the interactive voice response applications designed to provide phone-based call routing and self-service. The author, a leading human factors engineer, covers both high- and low-level decisions and also includes VoiceXML code examples.