The longevity and persistence of regional problems in the UK make them unusual among countries at a similar level of development. Certainly when compared to the USA it is surprising that the same regions have been relatively depressed throughout most of this century. While other countries, and notably Italy, have lagging regions which have never fully or successfully industrialised, the UK is again unusual in that it has a long-standing problem in regions which were formerly by-words for industrial progress. It is also surprising, given the stability of the problem, that it is not better understood. During the era in which Keynesian ideas dominated economic thinking in the UK the emphasis tended to be on the role of industrial structure. Some industries in national or international decline just happened to be located in the northern half of the UK or in Wales. Even though every empirical study found industrial structure to be only part of the explanation, the residual factors remained largely a mystery.