Popular media and recent consumer products give the impression that virtual reality (VR) is mostly about being tethered to a computer with a head-mounted display (HMD) covering the face, headphones over the ears, and some sort of controller in either hand for interaction. While this is indeed one valid incarnation of a VR system, it is not the only one. VR can be defined fairly broadly as synthetically generated sensory impressions (e.g., video, images, sound, touch) that are intended to immerse the users in an artificial, simulated, and interactive environment. This entry defines VR and discusses its history, hardware, and applications.