The Treaties set up an integrated judicial system between national courts and the European Court of Justice (ECJ), in which national judges are at the forefront of the application of Community law in the Member States. The co-operation between national courts and the ECJ is organised by the procedure of reference of national cases to the ECJ for preliminary ruling on the interpretation and on the validity of EC rules, provided for in art. 234 EC. The note analyses the scope of this provision, the conditions of its use by national courts and the consequence of the preliminary reference on national law. The note further investigates the question of liability of national judges for failing to request a preliminary ruling by the Court of justice. ...