Economic development and wealth vary across the space (Petrakos et al, 2005) and without proactive policies to reduce the differences these tend to increase. Hence, the European Union (EU) devotes a very important fraction of its budget to the regional policy ¾a 35.7 per cent of the total EU budget for the period 2007 to 2013 (European Parliament, 2006)¾ in order to reduce regional disparities across the Union and well-being disparities among citizens.
            Among the three main financial instruments of EU regional policy, the European Regional Development Funds (ERDF) ¾which is aimed at helping to redress the main regional imbalances in the Union (OJ, 2002, article 160)¾ is the most important EU regional policy tool and deals with the main regional cohesion goal: Convergence. This objective absorbs the best part of the regional budget and its relative weight has been increasing with the successive UE enlargements, to reach 251,163 million 2004 euros ¾almost 82% of total cohesion funds¾ in the period 2007-2013 (DO, 2006, art. 19).
            The list of regions and areas eligible for funding are chosen from the NUTS2 European regional classification, using regional gross domestic product per inhabitant as variable of reference. Therefore, the fact of being subventionable depends crucially on being on the list. However, although the EU has fixed some criteria to consider a region as NUTS2, the truth is that there are many regions that do not fulfil the requirements and that the geo-administrative criteria followed in each country have produced regions with sizes really very heterogeneous. This paper tries to put on the light these differences and to show how sensitive the selection method is to the level of geographic aggregation used.
KEYWORDS: EU-27, regional policy, NUTS regional classification.