A natural user interface (NUI) refers to an interface that is effectively invisible or becomes invisible with successive learned interactions. Current and next generation development of computer games, mobile devices, and desktop applications feature 3D interaction. This book deals with NUI design for the input hardware such as multi-touch, Kinect, wiiMote, and others, with the output as a regular display producing 3D graphics. The key attraction of this book is the hands-on approach and the affordability of the hardware used. Using C++ and Open GL to code the examples, this book can be used by beginners from Chapter 1 to the end or by experienced developers who require some of the more advanced chapters in their work. The word "natural" refers to the user experience?that the interaction comes naturally, while interacting with the technology. 3D NUIs are found in computer-aided design, radiation therapy, surgical simulation, data visualization, and virtual-reality entertainment.