Abstract The article focuses on damages liability between private parties—referred to as horizontal liability—that is based on EU law. Generally, this kind of liability may be based on EU secondary legislation or be derived from substantive EU law and legal principles. The article seeks to analyse the latter: liability in an area of EU law where so-called procedural autonomy still, at least apparently, prevails. Special attention is paid to the lively interface between EU law and national remedies and to the increasing EU law requirements for the enforcement of EU law in national courts. Recent case-law on private liability for damages caused by competition infringements is discussed as part of a more general question concerning the ways in which the relationship of EU law and national enforcement frameworks is developing.