Advances in human-computer interaction (HCI) technologies have led to emerging computer game systems that foster physical exertion as part of the interaction; we call them exertion games. These games highlight a body-centric perspective on our interactions with computers, in contrast to traditional mouse, keyboard and gamepad interactions, not just in terms of their physical interface, but also in terms of the experiences that they support. As a result, exertion games show great promise in facilitating not only health benefits, but also novel play experiences. However, to realize this promise, exertion games need to be well designed, not only in terms of technical aspects involving the sensing of the active body, but also in relation to the experiential perspective of an active human body. This article provides an overview of existing work on exertion games, outlines a spectrum of exertion games, and presents an analysis of key enabling technologies. We also position exertion games within a broader HCI context by reviewing and examining different design approaches and frameworks for building exertion games. Finally, the article concludes with directions for future work.