This article re-examines the utility of the idea of ‘fifth nation’ as a way of conceptualising the contemporary United Kingdom. The term appeared first in published form in the introduction by Peter Madgwick and Richard Rose to their jointly edited book, The Territorial Dimension in United Kingdom Politics (1982).There, Madgwick and Rose thought that ‘the United Kingdom is a fifth “nation” in Westminster’. In Understanding the United Kingdom published in the same year,Rose provided a different stress: Parliament ‘is, as it were, the fifth nation of the United Kingdom’. It is the argument of this article that ‘fifth nation’ still captures an important truth about the United Kingdom, but that devolution involves a shift in emphasis from the definite to the indefinite article. The first part of this article considers the character of the United Kingdom as the fifth nation as Rose (andothers) defined it. The second part considers how devolution challenges the comprehension of that idea. The final, and more speculative, part suggests that to understand the United Kingdom in some respects as a fifth nation may be more appropriate in contemporary circumstances.