Fictional games are games found in works of fiction such as novels, films, or TV series, that were designed specifically as part of those fictional worlds. Games such as Quidditch in the Harry Potter saga or Star Wars' Holochess are not merely additions to already rich universes, but exist as narrative devices that spark the reader or viewer's ludic imagination. In the book "Fictional Games. A Philosophy of Worldbuilding and Imaginary Play" (Bloomsbury, 2022), we have discussed the relevance, uses, and philosophical implications of nesting games within narratives, and have conducted design analyses on a number of fictional games. In this lecture I will present some of the findings of the book and offer a theory of fictional games as unique objects that are relevant to disciplines such as game studies, the philosophy of fiction, and media studies.