Provides a reading of the literatures on multi-level governance and federalism to develop a series of propositions about the nature of the relationship between different levels of government in the devolved United Kingdom.• Drawing on a survey of local government officers in Wales, the article reports support for both layer cake and marble cake interpretations of multi-level governance. • The article concludes with a discussion of the applicability of these models to our understanding of devolution in the United Kingdom.Since the United Kingdom began its devolution programme in 1999 governments operating at four different territorial scales-embracing the EU, the UK, the national and the local-have played a part in the governance of Wales. Multi-level governance of this type can be likened to a layer cake, in which each government operates in its own distinct jurisdiction, or to a marble cake in which governments have overlapping and interlaced responsibilities. Drawing on a survey that asked senior officers in Welsh local government to rate the impact of different levels of government, this article finds support for both interpretations of multi-level governance. Although largely discredited as a description of American federalism, the layer cake simile may have a new lease of life in the analysis of Europe's devolved nations and regions.