The result of four years of intensive research in a large multimodal dialogue project involving 12 partners from academia and industry, SmartKom is one of the most advanced multimodal dialogue systems worldwide and is a landmark project in the history of intelligent user interfaces. The system provides symmetric multimodality in a mixed-initiative dialogue system with an embodied conversational agent. The same software architecture and components are used in three fully operational application scenarios. The theoretical and practical foundations of SmartKom represent a new generation of multimodal dialogue systems that deal not only with simple modality integration and synchronization, but cover the full spectrum of multimodal dialogue. With contributions by leading scientists in the field, this book gives the first comprehensive overview of the results of this seminal project.