This article reads contemporary Catalan nationalist discourse through the lens of Tom Nairn’s polemical classic The Break-Up of Britain. First published in 1977, that text presents key issues for understanding contemporary Catalonia. The first is the emergence of a national sentiment that is separate from that of anti-colonialism because it is characterized by a higher level of economic development than the place it is seeking to break from, but is the repository of a legitimate claim to self-determination. That is how Nairn sees the Northern Ireland–Éire relationship, and that is a good analogy for Spain–Catalonia. The second is the tension between what he sees as ‘indifferent’, that is to say strictly civic-political nationalism and a more linguistically or culturally-driven nationalism. This is also a key tension in Catalonia, where immigration has transformed the national movement towards an interculturalist ideology and a de facto bilingualism (with Catalan and Spanish) remains a key but strategically unacknowledged element of that movement. The third aspect of Break-Up, and the synthesis of the comparison, is the importance of federalism, which is key for Nairn in seeing a way forward for the constituent countries of the UK and long a crucial, if not the crucial, political element of catalanisme.