Throughout the twentieth century, the principle of ’self-determination’ had many lives – as political catch-phrase, legal possibility and a justifying logic of world order. In the aftermath of the First World War, it was a principle that suffused the treaty discussions of the Paris peace conference, and loomed large in the framing of the plebiscites, as well as the League of Nations mandate system. This was not least because it animated the claims of numerous nationalist and anti-imperialist activists agitating for increased rights and freedoms in this moment. This chapter explores how the notion of self-determination, and related ideas around national belonging, race and gender, manifested in this 1919 moment in the promises of the Allied leaders, in the claims-making of non-state actors and in the discussions of legal professionals. In so doing it shows how we can understand particular visions of international law in this period as part of a much larger political and cultural conversation about the relationship between the state and national, racial and gendered belonging.