Knowing that the European Union, as an union of sovereign states, was incorporated in the form of an international organization with competences higher than the state’s, seeing also that it has international legal personality, being a subject of international law, the sovereign of its States had suffered a substantial decrease. The European Union has the legal capacity to conclude treaties (ius tractum), to maintain relations and to be represented in its relations with the other international law subjects; having its own identity, it is one of the members of the international society that has a common exterior policy and security; at the same time, its obligations are opposed to the other member states that it has to comply with and execute. Consequently, member states maintain their sovereignty, being always subjects of international law, but their legal capacity to act at international level has been restricted. These states have a special status. EU is an union of sovereign states. The relations between EU and these member states are of special subordination nature for the latter (especially for the states that have been already collectivized); the Union undertakes on their behalf (any treaty that goes through the Union obliges the states; coexistence on the international stage of the Union with member states supposes a common exterior policy that is established at the level of the Union. Member states may conclude treaties with third party states and with international organizations to the extent in which this competence does not belong exclusively to the Union and to the extent of these treaties compatibility with their obligations undertaken as a member of the Union. The case of member states is particular because European integration supposes a legal adjustment – structural and functional.