Both adults and children have the ability to not only think about reality but also use their imaginations and create fictional worlds. This article describes the process by which world creation happens, drawing from philosophical and psychological treatments of this issue. First, world creators recognize the need to create a fictional world, as when starting a pretend game or opening a novel. Then, creators merge some real-world knowledge with the premises of the fictional world to construct a fuller representation, though (...) there is some controversy about how much of the real world is represented in any given fictional world. After the world is created, events can be set in motion within it. While it is generally accepted that this basic process is used for a wide variety of fictional worlds, including fictional stories, pretend games, and counterfactual scenarios, this process of world creation can vary over the course of development and depending on the use to which it is put. (shrink)