This paper argues that the impact of devolution has been largely misperceived in both liberal intergovernmentalist (LI) and multi-level governance (MLG) accounts of European Union (EU) politics. To address the shortcomings of both LI and MLG, a new data set measuring institutionalized regional involvement in the domestic EU policy-shaping process in the EU-27 is presented. Analysis shows that the relationship between devolution and institutionalized regional involvement is overall positive but non-linear, with a strong threshold effect that is best captured by a quadratic function. The causal nature of the link between devolution and institutionalized regional involvement is ascertained through qualitative means using process tracing and Mill’s method of difference. The article concludes with the necessary updating of MLG and LI frameworks to account for the impact of devolution on EU policy-shaping.
