The article is devoted to the study of the principles of law that determine the fundamentals of the EU functioning. The concepts of general principles of law, international principles of law as well as principles of EU law are distinguished. The principles of EU law are classified into international, democratic, economic, organizational, functional, sectoral. The study of the principles of EU law is important for Ukrainian science in the context of Ukraine's integration into the EU. The results of the research will help the judiciary to integrate the principles of EU law into its case law. The Constitutional Court of Ukraine and the Supreme Court will play an important role in the integration of EU law into the national legal order. The following definition of the concept is proposed: the principles of EU law are the fundamental ideological principles of the EU legal system, which determine legal status of the EU as a subject of law and international relations; legal status of EU citizens; basic principles of organization and functioning of the EU; areas, limits and mechanisms for exercising the powers of the EU institutions; principles of legal regulation in the areas that fall within the competence of the EU. The principle of conferral is singled out as a fundamental functional principle from which other principles of EU law originate, namely: the principle of coherence of policies and actions; the principle of open EU cooperation with Member States; the principle of subsidiarity; the principle of proportionality; the principle of open cooperation between EU institutions; the principle of institutional balance. Their relationship and the mandatory nature of compliance are established. The operation of any of the institutions contrary to the principle of conferral or any of the principles named is a ground for appealing against such actions before the Court of Justice. According to Article 263 TFEU, the Court of Justice has the jurisdiction to review the legality of legislative acts, decisions or actions of the European Council, the European Parliament, the European Commission and the European Central Bank, as well as bodies, offices and agencies intended to produce legal effects vis-à-vis third parties. The content of the functional principles of EU law is revealed and the order of their application by the Court of Justice of the EU is analyzed on the example of one of the decisions. The classification of principles of EU law on a source of their placement is offered. In the system of principles of EU law should also be distinguished: 1) the principles of law that follow from the provisions of international law (the principle of peaceful cooperation and the principles of the UN Charter); 2) the principles of law derived from the principles of market economy and social policy (the principle of economic, social, territorial unity of the Member States and solidarity between them); 3) the principles of law derived from democratic principles (principle of respect for human dignity, freedom, representative democracy, equality, rule of law, respect for human rights, including the rights of minorities). Therefore, in a general sense, the system of principles of EU law includes: international principles of law, general (democratic principles of law, economic principles, principles of EU law) (organizational, functional, sectoral). KEYWORDS Key words: general principles of law, principles of EU law, EU Court of Justice, the principle conferral, EU goals