the judicial branch of the European Union (EU). Its headquarters are in Luxembourg. The ECJ originated in the individual courts of justice established in the 1950s for the European Coal and Steel Community, the European Economic Community, and the European Atomic Energy Community. The function of these courts was to ensure the observance of law in those organizations' interpretation and application of their treaties. In 1958 a single, unified ECJ was created to serve all three of the European Communities (later called the European Community). In 1989 the Court of First Instance was established to reduce the court's workload.

The ECJ reviews the legality of the acts of the Commission and the Council of Ministers of the EU, which are the executive bodies of that organization. The court typically hears cases involving disputes between member states over trade, antitrust, and environmental issues, as well as issues raised by private parties, compensations for damages, and so on. The court has the power to invalidate the laws of EU member states when those laws conflict with EU law. The ECJ serves as the final arbiter of the growing body of international law that has accompanied the economic and political integration of Europe. The court's full bench consists of 25 judges, who are appointed to renewable 6-year terms, and 8 advocates-general. Prior to 2004, the ECJ met as a full chamber for all cases, but it now may sit as a “grand chamber” of 11 judges.