This work elaborates the issues related to the Court of Justice of the European Union as one of the basic institutions of the European Union, defining the European Union itself together with its main institutions, and also interpreting essential terms concerning the European Union law. The Court of Justice of the European Union is the institution of the European Union that encompasses the whole judiciary. It is seated in Luxembourg and includes: The Court of Justice, also known as European Court of Justice, the highest court in the European Union legal system; The General Court (created in 1989., formerly called the Court of First Instance); The Civil Service Tribunal, a specialized court created in 2004.The mission of the Court of Justice is to ensure that the law is observed in the interpretation and application of the Treaties. The Court reviews the legality of the acts of the institutions of the European Union, ensures that the Member States comply with obligations under the Treaties; and interprets European Union law at the request of the national courts and tribunals. In conclusion, the Court constitutes the judicial authority of the European Union and in cooperation with the courts and tribunals of the Member States, it ensures the uniform application and interpretation of European Union law.