The monograph is the first in the Ukrainian science of international law comprehensive study of trends and problems of application of international law in the Ukrainian-Russian interstate relations throughout the period of their existence. The monograph offers an analysis of key features, issues, trends and patterns of transformation of international legal interaction between Ukraine and Russia at all historical stages and in basic spheres including the forms of their mutual influence. The author identifies features of the treaty framework and institutional mechanisms of regulation of bilateral relations. The international legal positions of Ukraine and Russia in respect of all sensitive issues of relations, starting from Crimea and ending with the problem of delimitation and demarcation of borders, are studied. The author offers an understanding of the problem of applying international law in the Ukrainian-Russian bilateral relations; gives legal qualification of the parties’ actions during the interstate conflict between Russia and Ukraine in 2014–2016; summarizes the practice, outlines the drawbacks and provides recommendations regarding the refinement of Ukraine’s actions in applying international legal means of responding to the Russian aggression; works out the basic principles of the international legal regulation of Ukrainian-Russian relations upon the end of the conflict and of the application of the rules of international legal responsibility. The book is intended for everyone interested in contemporary issues in international law.