The decentralised system for the application and enforcement of European Union law depends on the national courts of Member States. When fulfilling this function of ‘EU law court’, national courts aim for the effective application of EU law and the judicial protection of the rights of individuals, which they derive from EU law. The involvement of national courts in the decentralised application of EU law rests on the principles of primacy and direct effect, completed by the principle of consistent interpretation. Still, the dialogue between the Court of Justice of the European Union and national courts, on the EU duties of national courts, is constantly developing, as the evolution of social, economic, and legal circumstances provokes new challenges to the jurisdictions across the European Union. The chapter presents the reasons for undertaking the research in the case-law of national (Polish) courts concerning the application of EU law in domestic legal order, which is the authors’ strong conviction on the necessity to perceive EU law via the prism of national legal cultures. Additionally, the chapter explains the scope of the analyses, the results of which are presented in this book, which is the application of the principle of consistent interpretation and the principles of primacy and direct effect of EU law provisions. It also includes presentation of the general legal framework of Polish justice system, the main branches of the judiciary and their competences. The chapter concludes with presentation of the method applied for the analyses, the results of which are presented in this book.