Nations in flux explores the evolution of territorial politics in Catalonia and Scotland since 2010, offering an in-depth, comparative analysis of developments in both cases and drawing on interviews with political elites whilst providing a compelling snapshot of the growing relevance of nationalism in contemporary society and politics. Empirically, this book analyses the experiences and effects of referendums on independence, Brexit and the COVID-19 pandemic, and examines some of the most pressing tensions within the existing territorial models. It highlights the need for further reform in both cases and identifies necessary changes to ensure the institutionalisation of more accommodative territorial models and thus, the continuation of political partnership between Catalonia and Spain, and Scotland and the UK. Overall, the book raises important questions about the accommodation of diversity in plurinational states in the twenty-first century.