The article is devoted to the theoretical and legal analysis of the principle of inviolability of borders as an important aspect of modern international relations, clarifying the role of this principle in ensuring the sustainability of international law and order, especially in the context of Russian aggression against Ukraine, as well as determining the main directions of activity of international organizations to support the Ukrainian people in their struggle for the liberation of their own territories captured by the Russian Federation. An analysis of the main stages of institutionalization of the principle of inviolability of borders has been carried out, the prerequisites for its formation and peculiarities of development in the system of modern international law have been determined, its international legal consolidation and normative content have been disclosed. It is stated that the inalienable and conscientious implementation of the principle of inviolability of borders by all subjects of international law is recognized as an objective necessity, since in the conditions of modern international relations, state borders play an essential role in determining the boundaries of sovereignty, territorial integrity and independence of each state. It is noted that since the proclamation of independence, the Ukrainian state has faced an unsettled problem of contractual and legal registration of state borders with numerous European countries and former Soviet republics, which also declared their independence. It is stated that the most difficult was the settlement of issues related to the definition and contractual and legal registration of borders with the Russian Federation, especially in the context of its destructive position in Crimean peninsula issues. Considerable attention is paid to the violation of the principle of inviolability of borders in the context of the armed conflict between Ukraine and the Russian Federation. It is proved that Russia’s gross violation of the principle of inviolability of borders has become one of the main security problems on the European continent. This was due to the aggressive actions of the Russian Federation, including the annexation of the Crimea, Luhansk, Donetsk, Kherson and Zaporizhzhya regions, as well as disregard for all the requirements arising from this principle. It is noted that such a violation of the principles of international law has caused a significant resonance in the world and has important consequences for security and stability in the region. The article analyzes the activities of international organizations (UN, Council of Europe, European Union, Organization for Security and Co-operation in Europe) as a response to the violation by the Russian Federation of the principle of inviolability of borders by committing unprovoked armed aggression against Ukraine with subsequent annexation of Ukrainian territories. The normative legal documents adopted by these international organizations aimed at supporting the territorial integrity of Ukraine within its internationally recognized borders are considered in detail.