"First-Person Shooter computer games are designed to be immersive experiences yet the phenomenon of immersion is little understood. This article surveys theories of immersion in virtual worlds and examines FPS game elements that might contribute to the state. The roles of attention and positive feedback in facilitating player immersion in FPS games is explored. In particular, the role of selective attention is highlighted before the article finishes with a discussion on the design of immersion in FPS games using the principles presented here."