European integration is a direct response to the tragic historical events of the early 20th century. It creates political ties and a new legal system with a diversified nature. Regulation of more and more new areas within the process of strengthening European integration is a response to a challenge of the future as well as a binder of domestic legal identities. The article deals with a broad subject-matter of multilevel nature of European laws and its constitutional role. The basis for the examination is the presentation of the achievements of the doctrine and the author's analysis of the issue, constituting the specificity of the subject, supplemented by an analysis of commonly known and less ‘popular' decisions of the European Court of Justice.