How can we measure and explain the salience of European integration for political parties? Although salience is an extensively used concept within the field of European Union (EU) studies, it suffers from conceptual ambiguity and lacks rigorous empirical investigation. This article sets out to conceptualise and explain the salience of European integration to political parties, by cross-validating three empirical salience measures used in the Comparative Manifesto Project, European Election Study and Marks/Steenbergen Expert survey. The analysis demonstrates that whilst one common dimension underlies the different salience measures, there is no common explanation for variation in salience. There is one exception: when the EU is salient to the party system as a whole, it tends to be salient to each party in the system. © 2006 Elsevier Ltd. All rights reserved.