After the end of the existence of the Soviet Union, the legal framework developed by Persia and the USSR lost its relevance. However, the legal agreements reached have established a legal basis for the orientation of negotiation mechanisms in a five-sided format. After having analyzed the agreements reached during the period of bilateral relations and assessing them with modern geopolitical processes. The formation of the fundamental principles of relations in the region during this period should be taken into account. From the point of view of geopolitical regional processes, key political events on a global scale taking place in this period (the Islamic Revolution of 1979 and the collapse of the socialist camp) formed the foundations of the geopolitical realities of the modern Caspian region. This paper analyzes the main legal documents concerning the Caspian region reached in the XX century, taking into account the influence of the heritage of the last century on modern geopolitical processes in the region of the Caspian Sea. Аnalyzing bilateral and five-sided legal documents affecting the Caspian Sea, it is necessary to highlight the commonality of the approach in determining the legal status of the Caspian Sea. This issue, after the termination of the existence of the bilateral platform, was a priority task. It is necessary to highlight that, before the five Caspian states reach a convention on the legal status of the Caspian Sea. The regulatory factors in the region of the Caspian Sea were the provisions of legal documents between the USSR and Iran, it is important to highlight the key ones: the treaty between the RSFSR and Persia of February 26, 1921 and the treaty on trade and navigation between the USSR and Iran of March 25, 1940.
