Abstract: This thesis explores the multiple ways in which non-binary people negotiate their identities, their authenticity, and their embodied experiences through language. Twenty-two non-binary-identified people living in the UK were interviewed for this project. Those same participants also provided writing samples which were included in the analysis. Additionally, a 2.9 million-word corpus of non-binary language was analysed using corpus linguistic tools. This thesis theorised gender as something one becomes rather than something one is (Linstead and Pullen, 2006), a relational process through affective intensities which move through the body, society, language, and other material and abstract elements. Drawing from assemblage theory (DeLanda, 2006) and Deleuze and Guattari’s (1987) materialist ontology, which acknowledges the multiple (linguistic and material) components that merge at particular points to produce (or assemble) a becoming, I identified the most significant affective intensities which aided in the (de/re)territorialisation of non-binary gender becomings, or the non-binary-assemblage. Furthermore, the theory of linguistic becomings, which refers to the discovery, adoption, (re)assessment, and ongoing social negotiation of gender-related language, was developed in this thesis. The linguistic parameters of non-binary identities were found to be constantly reassessed, redefined, and renegotiated. A variety of material embodiments – and their relationship to language – were also identified, including affective fluidity and neutrality, and dysphoria. This thesis also explores the ways in which non-binary people in the present study navigated the world using non-binary language, the distress that originated from social interactions in which their language was not affirmed (i.e., misgendering), and the various ways in which they managed these situations. Overall, this research found that utilising a distinct type of language – a linguistic becoming – not only served as a tool to differentiate their gender and territorialise their identity, but also as a marker of social identity and group membership, thus allowing their identities to be recognised and more widely validated.