A pervasive game is one where the gaming experience is extended out in the real world, or where the fictive world in which the game takes place blends with the physical world. The "It's Alive" mobile games company described pervasive games as "games that surround you", while Montola, Stenros and Waern's book, Pervasive Games defines them as having "one or more salient features that expand the contractual magic circle of play spatially, temporally, or socially." The concept of a "magic circle" draws from the work of Johan Huizinga, who describes the boundaries of play.