A 3D user interface (3DUI) is an interface in which the user performs tasks in three dimensions. For example, interactions using hand/body gestures, interaction using a motion controller (e.g. Sony PlayStation Move), interaction with virtual reality devices using tracked motion controllers, etc. All these technologies which let a user interact in three dimensions are called 3D user interface technologies. These 3D user interfaces have the potential to make games more immersive & engaging and thus potentially provide a better user experience to gamers. Although 3D user interface technologies are available for games, it is unclear how their usage affects game play and if there are any user performance benefits.  This book presents state of the art research on exploring 3D user interface technologies for improving video games. It also presents a review of research work done in this area and describes experiments focused on usage of stereoscopic 3D, head tracking, and hand gesture-based control in gaming scenarios. These experiments are systematic studies in gaming environments and are aimed at understanding the effect of the underlined 3D interface technology on the gaming experience of a user. Based on these experiments, several design guidelines are presented which can aid game designers in designing better immersive games.