INTRODUCTION. For 74 years, Russia and Japan have both claimed legal title over the four Southern Kuril Islands, paralysed by their controversy from making a post-WWII peace treaty and realising the full potential of their bilateral relations. This entire time, the islands have been governed in all aspects of their legal, political, and economic life, by the Russian side. This entire time, Japan has made diplomatic protests contesting the legality of Russian jurisdiction. With no international authority to determine which of the countries prevails, one wonders if the effective Russian control has not or should not have, by now, overcome Japanese protests – almost the only tool international law provides for states to prevent another’s title. MATERIALS AND METHODS. The international legal principles and doctrines at play are the overarching notions of effectiveness and stability, governing the resolution of any territorial disputes, the related doctrines of prescription and acquiescence, and the maxim ex injuria jus non oritur that aims to preclude territorial change if it originates in illegality – these are studied on the basis of contemporary works on the international law of territory and the general scientific methods of analysis, synthesis, description, and deduction. RESEARCH RESULTS. Effectiveness and stability lie at the heart of territorial change. Their derivative doctrines of prescription and acquiescence serve as tools for legitimizing title of dubious origins through long, peaceful and effective possession of territory absent protests from the former sovereign (and subject to the self-determination of the territory’s inhabitants), and, possibly, with the help of recognition by third states. Whether the opposing notion of ex injuria jus non oritur is an international legal principle remains debatable. The international law, however, in the politically sensitive matters of territory is too meek to provide a definite answer to when these concepts clash within the reality such as that of the Southern Kuril dispute. DISCUSSION AND CONCLUSIONS. In weighing the Russian effective control over the islands against Japan’s demands that the territories be returned to Japan, the key question is: does effective possession override protests, given the duration and quality of such effectiveness and such protests? It is argued here that such an answer would benefit the aim of stability sought by the international law and that in the situation at hand it should be a carefully qualified, but emphatic yes.