Solidarity in EU law:an elusive political statement or a legal principle with substance?

Solidarity, although widely used in EU legislation and the early jurisprudence of the Court of Justice of the European Union (CJEU), lacks a clear meaning. It appears as an amorphous concept whose contours change depending on the legal areas and the actors involved, and which generates differing levels of commitment. This article explores the attributes common to the different expressions of solidarity as a binding legal obligation in order to develop European solidarity as an integrated concept. It examines the meaning and boundaries of solidarity by focusing on the reasons that generate solidarity obligations under the EU Treaties and by analysing the case law where the CJEU has drawn on solidarity or could have drawn on it, but decided not to do so. The article concludes that while different aspects of solidarity are embodied in EU legislation, the concept has normative force mainly when it is driven by self-interest in a reciprocal relationship. Although references have been made to its ethical underpinnings, in the absence of a reciprocal return, the normative premises of solidarity have remained weak