The course aims to provide an overall understanding of European Union law. It starts with an introduction, which focuses on the integration process through the modification of the treaties and the enlargement. It highlights the peculiarities of the European Union as a legal order and a “community of law”, with respect to the phenomenon of international organization. The analysis also covers the free movement of people and the European citizenship. Then, the European institutional framework is examined, taking into account the relation between the Institutions and the principles guiding their interaction. The toolkit adopted by the Union to overcome the democratic deficit is illustrated, including the decision-making procedures for the adoption of EU acts. Then, the course focuses on the principles which regulate the attribution and the exercise of EU competences and the forms of differentiated application. The hierarchy, features and functioning of EU sources is then introduced and explained in its relations with domestic law. The notions of primacy, autonomy and direct effect of EU law are widely investigated, alongside the modalities for the implementation of EU law in national legal orders, in particular in Italy. Finally, an in-depth examination of the functions of the EU Court of Justice is carried out, with peculiar emphasis on the preliminary ruling as an instrument of dialogue between the courts.