The main topic of this volume is natural multimodal interaction. The book is unique in that it brings together a great many contributions regarding aspects of natural and multimodal interaction written by many of the important actors in the field. It is a timely update of Multimodality in Language and Speech Systems by Björn Granström, David House and Inger Karlsson and, at the same time, it presents a much broader overview of the field. Its 17 chapters provide a broad and detailed impression of where the fairly new field of natural and multimodal interactivity engineering stands today. Topics addressed include talking heads, conversational agents, tutoring systems, multimodal communication, machine learning, architectures for multimodal dialogue systems, systems evaluation, and data annotation.