The publication presents an introduction to the European Union law. It provides information about functioning of the European Union and analyses the constitutional and institutional concept of the European Union. The publication covers the following areas of the European Union law: definition of the European Union, historical development of the European Communities and the European Union, obligations of the member states arising from the membership in the European Union and the competences of the European Union. An important part of the publication deals with the nature of European Union law, sources of European Union law and its effect. The reader also acquires information about the institutions of the European Union and about their powers and composition. The publication is especially interesting for the students, but also for lawyers who are interested in obtaining an insight on the European Union and the legal order of the European Union.