Abstract: The research object is correlation and contradiction between the fundamental principles of modern international relations: the right of people to self-determination and the principle of the state sovereignty. The problem of Catalan self-determination in Spain is the result of such contradiction. This problem is one of the key issues of Spain’s policy; with the development of the EU as a political association, it’s become an important issue on the European agenda, too. It is not only the matter of self-determination, but it is also the matter of possibility to form a new independent state after the referendum scheduled for October 2017. The complexity and ambiguity of the issue is worsened by the difference between the positions of the key actors of the problem: the region, Spain and the EU. The author studies these positions. The author uses the methods of indirect and instrumental monitoring. It is based on the sources of the EU and the Government of Catalonia. The author uses the results of the interviews of Spanish specialists in this problem. The author concludes that the key method of the problem settlement should be constructive negotiation process with the participation of the representatives of the EU, the governments of Spain and Catalonia. At the present time this instrument is not used, and the parties to this conflict confirm it. Besides, the position of the EU on the problem of unilateral secession of Catalonia remains firm: the EU doesn’t accept unilateral secession of regions from the EU member-states. If it happens, the citizens of such regions will not be the citizens of the EU anymore.