The article deals with the most important theoretical and practical issues of the realization (implementation) of international law, examines the concepts, forms and content of the realization (implementation) of international law, finds out the reasons that affect the inefficiency of international law. It is noted that the realization (implementation) of the norms of international law includes two levels: international (collective activity of states) and national (individual activity of the state). Particular attention is paid to the importance of the implementation of the norms of international law and their primacy both over domestic law and over politics in international relations. It is mentioned that in international law the UN Charter enshrined the principle of conscientious observance of international obligations (pacta sunt servanda), which extends its effect to all norms, regardless of functions, purpose, form of expression. According to this principle, each state must fulfill in good faith its obligations arising from the generally recognized principles and norms of international law and specific international treaties. The article argues that this principle is mandatory not only in relations between states, but also extends to the sphere of national law in the context of the implementation of international law. The article emphasizes that in modern conditions the solution of global problems of peace, the stability of the international order, as well as the solution of many domestic problems in the literal sense depends on the effectiveness of international law. An opinion is expressed about the need to develop a unified science of the law of both domestic and international law. Since, just as it is correctly noted in the legal literature, the issues of the realization (implementation) of international law are shifted from the international to the national sphere, due to the fact that a significant number of international legal norms are intended for final implementation within states. Such a statement is true in relation to all branches of international law, in particular in the field of human rights and the protection of the environment. It is indicated that in order to fulfill international obligations, it is required from the state on a national level to ensure the harmonization of their laws and practices with obligations under international law.