During the 20th century self-determination has become one of the most important principles of international law and one of the most prominent rights on the basis of which (all) peoples can decide freely on their political status and their economic, social and cultural development (Article 1 common to the 1966 ICCPR and ICESCR).Whereas the idea of self-determination is envisaged as an advanced concept aimed at the liberation of peoples under foreign domination in the process of de-colonisation, today's situation and reality call for its reconsideration and adequate clarification with respect to the issues of who is entitled to the right of self-determination and in which forms and to which extent it can be exercised if seen from the aspect of the impact which its exercise might have on the integrity of states. This call is strengthened by the fact that all contemporary states have certain complexity with respect to their national/ethnic/religious/linguistic or racial composition. One of the basic problems in the application of the right of self-determination is created by the fact that there are no definitions in international law on the concepts of various groups. There is no clear answer on what are peoples who are entitled to the right of self-determination, nor is there an accepted definition for other groups which are politically relevant, like indigenous peoples and/or minorities. This may cause serious difficulties since such a lack of clarity provides conditions for persistent claims on the part of groups other than peoples on the right of self-determination, which sometimes threatens territorial integrity of states.