The role of the Constitutional Court in the redefinition of policies, and in particular of decentralisation, has been scarcely analysed in the European context, with studies focusing mainly on the US case. The aim of this paper is to contribute empirically and theoretically to this line of research by analysing the results of a unique dataset on constitutional preeliminary references (judicial concrete review) in Spain from the 1980s to the present. In particular, we look at the impact of concrete review by the Spanish Constitutional Court' rulings on the distribution of regional competences. Ordinary courts with judicial review capacity initiate cases with potentially important political consequences, becoming to a certain degree unelected political actors. This paper explores what are the conditions under which constitutionality preeliminary references are raised, specifically in the case of the Regional High Courts in Spain, and what are the implications for the whole system of governmental competences distribution. The paper follows a quantitative approach to explain what contextual and political factors may influence the likelihood that an ordinary judge will decide to trigger a particular preelimimary reference, and to understand the extent to which constitutional issues can potentially affect descentralization.