Modern constitutionalism is built from domestic application to the supranational level. This is due to many factors, including the common values of the EU member states. There is no doubt that states united by a certain union unite on the basis of certain values and criteria. Among which are the fundamental principles of constitutional law, which are discussed in this article.
 The first indisputable feature is the rule of law, which is considered in the article both at the level of EU member states and at the level of the European Union as a separate legal system, based on its institutional organization. The article also considers the means of control over the rule of law. In the EU there are purely declarative remedies in the form of Art. 7 of the EU Treaty are as effective as the Rule of law framework procedure, which is demonstrated in the article on the example of Poland and the conflict that arose over changes to the legislation on the Supreme Court. Such protection is important, as Article 2 of the EU Treaty contains a provision on the rule of law for states wishing to become members of the EU.
 The unobvious principle of constitutionalism is democracy, which is substantiated in this article. The European Union uses more than just classic examples of democracy, such as representative democracy, by delegating representatives to the bodies and institutions of the European Union. Of interest is the procedure of the European Citizen Initiative, which acts as an act of direct democracy, according to which EU citizens can directly influence the legislative process regardless of its stage, as well as submit initiatives on existing acts. It should be noted that this procedure, although reminiscent of a petition, differs from it in terms of its procedural design and conditions for submitting such an initiative, which has aroused interest in it in this article.