The article analyzes the phenomenon of national self-determination in terms of evolution and functioning. The authors aim to determine the general characteristics and evolution of this phenomenon in both conceptual and applied versions. In the evolution’s context of national self-determination as a theoretical concept and a political and legal principle, several stages were identified and considered. According to the authors, each stage of the phenomenon’s evolution was inevitably accompanied by its qualitative transformations, both in political and legal terms. The first stage (from the end of the XVIII c. till the First World War), according to the authors, is characterized by the emergence of the idea and the formation of the socio-political concept of national self-determination, and the applied aspect of the phenomenon of national self-determination is filled with concrete content based on the ever-expanding political practice of its application. The second stage (from the First World War and the post-war reconstruction) is characterized by the transformation of self-determination from a concept into a political principle. The authors associate the third stage of the evolution of the phenomenon of national self-determination (the period after the Second World War) with the development of international relations and the formation of a global bipolar system. National self-determination turned into a principle of positive international law and laid the foundations for the future political instability of the newly independent states. Finally, the last period (the early 90s to this day) is characterized by the search and crystallization of new approaches to the principle of national self-determination and the emergence of new theories, the authors of which are trying from a political and legal point of view to substantiate the legitimacy of an expansive interpretation of this principle. The analysis allowed us to conclude that the qualitative transformations of the principle of national self-determination presented in the article did not lead to the formation of the phenomenon of national self-determination as an integral, complete, and universally recognized international political and legal norm.