This paper explores what is known about the actual impact of the EU on sub-national (local and regional) government. Existing research on the impact of the EU on sub-national authorities appears to have a strong emphasis on the positive effects or the opportunities that emanate from the EU. By contrast, studies on European constraints that limit sub-national autonomy are rather scarce. Moreover, many studies fail to take sub-national government itself as the object of analysis, as a result of which most conclusions are rather hypothetical in nature. Trying to fill the lacunas in the existing literature, the authors present a conceptual framework that includes three dimensions along which the EU might influence sub-national decision-making: by enforcement or invitation, by hampering or improvement, and by obstruction or enabling. A pilot study found that nearly each of these types of influence was present, indicating the conceptual sensitivity and empirical relevance of the three dimensions. © 2006 Taylor & Francis.