Eye tracking is a process that identifies a specific point in both space and time that is being looked at by the observer. This information can also be used in real-time to control applications using the eyes. Recent innovations in the video game industry include alternative input modalities to provide an enhanced, more immersive user experience. In particular, eye gaze control has recently been explored as an input modality in video games. This book is an introduction for those interested in using eye tracking to control or analyze video games and virtual environments. Key concepts are illustrated through three case studies in which gaze control and voice recognition have been used in combination to control virtual characters and applications. The lessons learned in the case studies are presented and issues relating to incorporating eye tracking in interactive applications are discussed. The reader will be given an introduction to human visual attention, eye movements and eye tracking technologies. Previous work in the field of studying fixation behavior in games and using eye tracking for video game interaction will also be presented. The final chapter discusses ideas for how this field can be developed further to create richer interaction for characters and crowds in virtual environments. Alternative means of interaction in video games are especially important for disabled users for whom traditional techniques, such as mouse and keyboard, may be far from ideal. This book is also relevant for those wishing to use gaze control in applications other than games.