The Principal–Agent approach guides a comparison of the scrutiny and implementation records of the EU member states. The main argument is that there is systematic co–variation. Cross–nationally, an influential scrutiny process is associated with a strong implementation record. But because both of these variables also co–vary with the North–South dimension of EU politics, a fundamental challenge for future research is to evaluate the importance of existing between–country variation relative to the new Principal–Agent relationships that are emerging within the integration process.