This book demonstrates state of the art multi-modal interaction with modern inout devices. Currently, most application are uni-modal (e.g., touch) and in some cases bi-modal (e.g., keyboard and mouse). The challenge for developers and researchers: is how to improve interaction when using multiple devices. This book provides the necessary background and then presents case studies in multi-modal interaction. In addition to Interactive Paint, Microsoft Hololens is used to demonstrate the need for multi-modal interaction when using multiple input devices. This book presents an input perspective (as opposed to output like displays and head-mounted displays).