The concept of res judicata was introduced into European Community law very early on by the European Court of Justice and it remains an essential component both of EU procedural law and of the interactions between national procedural systems and EU law. It is a fascinating example of the inluence of comparative law on the ECJ and of this institutions normative powers. It is also at the heart of many conflicts with national courts, as EU law requires restrictions to national understandings of the scope of rules ensuring the finality of judicial decisions. Several recent judgments of the ECJ demonstrate that the issue remains important but also that litigants - and sometimes the Court itself - are not sufficiently aware of the rules established in the case law. A well-known and fundamental characteristic of any procedural system, this concept remains under-studied in EU law.
