This Element looks at adaptations of bestselling works of popular fiction to cinema, television, stage, radio, video games and other media platforms. It focuses on ‘transmedia storytelling’, building its case studies around the genre of modern fantasy: because the elaborate storyworlds produced by writers like J. R. R. Tolkien, J. K. Rowling and George R. R. Martin have readily lent themselves to adaptations across various media platforms. This has also made it possible for media entertainment corporations to invest in them over the long term, enabling the development of franchises through which their storyworlds are presented and marketed in new ways to new audiences.