A Tongue Not Mine examines the significance of bilingualism, translation, and self-translation in the work of Samuel Beckett. After a mid-career adoption of French as a language of composition, Beckett continued to write in his native English as well as French, and to translate his work systematically, though often unfaithfully, between the two. This study focuses on how Beckett's self-translation, rather than being an ancillary, essentially practical task of linguistic transfer, emerges as an integral component of his work's exploration of uncertainty and exile, and its critique of the myth of identity. His apprenticeship in literary translation of the work of others, his decision to write in a non-native language, and that decision's corollary of continual self-translation, emerge as central to the privileging of narrative gaps and disunities, and the struggle with language in his work. By demonstrating how the recurrent tropes of Beckett's mature writing - a profound linguistic scepticism; nomadic, evanescent, multiple subjects; the erosion of proper names and settings - emerge from the fact that he was constantly translating, both his own and others' work, throughout his career, Sinéad Mooney considers the work of this important Irish modernist from a neglected perspective. Bilingualism emerges as a generative force fundamental to Beckett's aesthetics of dislocation, in which identity and language are disarticulated. Informed by translation studies, analyses of literary bilingualism, and post-colonial theory, this study reconsiders the relationship between translation, modernism, and twentieth-century Irish literature.