This document discusses multimodal interfaces. It defines multimodal interfaces as those that process two or more combined user input modes, such as speech, gestures, touch, etc. It outlines some key characteristics of multimodal interfaces including exploiting multiple human senses and providing new functionalities. The document also covers guidelines for designing multimodal interfaces, such as supporting flexibility and adaptivity. Example application scenarios for multimodal interfaces in healthcare robots, education systems, and smart homes are also presented.