First ever critical study of Tolkien's little-known essay, which reveals how language invention shaped the creation of Middle-earth and beyond, to George R R Martin's Game of Thrones. This is an annotated edition of Tolkien's seminal 1930s essay 'A Secret Vice', in which he first revealed his 'vice' of inventing languages in his fantasy fiction. Tolkien's linguistic invention was a fundamental part of his artistic output, to the extent that later on in life he attributed the existence of his mythology to the desire to give his languages a home and peoples to speak them. As Tolkien puts it in 'A Secret Vice', 'the making of language and mythology are related functions', in fact 'coeval and congenital'. In the 1930s Tolkien composed and delivered two lectures in which he explored these two key elements of his sub-creative methodology. In 1931 he gave a talk to a philological society entitled 'A Hobby for the Home'. In this talk, later published as 'A Secret Vice', Tolkien unveiled for the first time to a listening public the art which he had both himself encountered and been involved with since his earliest childhood: 'the construction of imaginary languages in full or outline for amusement'. 'A Secret Vice' would be edited by Christopher Tolkien for inclusion in The Monsters and the Critics and serves as the principal exposition of Tolkien's art of inventing languages. But it has often been neglected by critics and this new critical edition will go some way towards re-opening the debate on the importance of linguistic invention in Tolkien's mythology and the role of imaginary languages in fantasy literature. In addition to all previously unpublished notes and essays by Tolkien connected with the essay, the book discusses the subject of Tolkien's languages in the wider context of modern fantasy, including the Peter Jackson Hobbit and Lord of the Rings films and Game of Thrones.