This preface tells the story of how Multimodal Usability responds to a special challenge. Chapter 1 describes the goals and structure of this book. The idea of describing how to make multimodal computer systems usable arose in the European Network of Excellence SIMILAR - "Taskforce for cre- ing human-machine interfaces SIMILAR to human-human communication", 2003- 2007, www. similar. cc. SIMILAR brought together people from multimodal signal processing...