This research investigates the attitudes and experiences of non-binary people towards legal sex recognition and reform in England and Wales. The thesis focuses on the Gender Recognition Act 2004 (GRA) which was pioneering at the time of its introduction. However, it has since been subject to criticism based on intrusive and burdensome requirements, and the lack of provision for non-binary identities. The thesis provides an original contribution to the existing scholarship on legal sex recognition by adopting a distinctly non-binary centred approach. The thesis presents empirical data on non-binary attitudes towards ‘macro-reform options’, namely additional sex options in law and/or decertification where the sex marker is removed from the birth certificate. Moreover, in recognising that non-binary people may still seek recognition of a preferred binary sex marker, this thesis also addresses a notable gap in the scholarship by presenting empirical findings on attitudes towards individual requirements of the GRA. Each chapter considers recommendations for reform according to a combined normative framework of critical realism and non-ideal theorising with a focus on policy-in-context. Seven individual reform recommendations are proposed which would essentially provide for legal sex recognition based on self-determination and introduce a third sex option. These proposals are analysed according to a human dignity-based conception of rights. The relationship between human dignity and non-binary rights has received relatively little scholarly attention, despite the role that dignity has played in developing trans rights across Europe. The empirical findings are contextualised within this dignity-based framework to draw out their significance further and to illustrate the opportunities of this framework for non-binary rights claims. The thesis concludes by calling for the seven reform recommendations to be adopted as they represent a fair balance between policy considerations and the need to provide non-binary populations with conditions which recognise their equal and intrinsic dignity.Economic and Social Research Council (ESRC)