This article analyses the circumstances under which the EU incurs liability for contributing to breaches of EU law committed by Member States. It proposes to distinguish between what will be called primary liability, i.e. the liability that directly arises from the violation committed by the Member State, and associated liability, i.e. the liability arising for having contributed to the Member State’s violation. Systematically analysing the ECJ’s case law on primary and associated EU liability for contributions to breaches of EU law, this article identifies patterns in the Court’s approach and ultimately provides a clearer picture of the conditions under which liability may arise.