The monograph aims to verify the thesis that the language rights of European Union citizens are an important element of the EU’s respect for the national identities of its Member States guaranteed in the Treaties. The protection of these rights has been consistently strengthened in EU law, with citizenship of the Union playing an important role in this process. The formulated thesis is verified mainly through the use of the dogmatic and legal methods, and the comparative legal method. The specific nature of the subject matter discussed requires an interdisciplinary approach, and the methods used in the field of linguistics are also applied mainly with reference to the conceptual apparatus adopted within the EU legal order.