The subject of the article.The article represents a research of conceptual properties and issues of applying reservations and declarations to the Multilateral Convention to Implement Tax Treaty Related Measures to Prevent Base Erosion and Profit Shifting, developed in frames of implementing the OECD/G20 Action Plan on Base Erosion and Profit Shifting (BEPS). The Multilateral Tax Convention modifies the application of agreements for avoiding double taxation, that are covered by its action. Since January 1, 2021 it has been applied to 34 agreements for avoiding double taxation between the Russian Federation and such countries as the UK, Canada, Latvia, Malta, the Netherlands and France. The Multilateral Tax Convention provides for updating bilateral tax treaties – whether they were developed upon the OECD Model Tax Convention or the UN Model Tax convention. The Convention retains a great degree of flexibility in relation to the implementation of its provisions – especially by the means of reservations, made by the countries.The purpose of the articleis to identify the main characteristics of applying reservations and declarations in international tax law.The methodology.The study is based on empirical methods of comparison and description, theoretical methods of formal and dialectical logic.The main results.Reservations have played a minor role in international taxation until now – usually they reflected disagreement, expressed by an OECD member country with the provisions of the OECD Model Tax Convention or its Official commentary. Reservations were formulated in relation to a non-binding (model) document and their importance was limited. Such reservations cannot be associated with declarations, made in relation to legally binding documents like the Multilateral Tax Convention. Analyzing the general points of scientific dispute upon the mentioned range of issues, the author argues with researchers who deem that the structure of reservations to the Multilateral Tax Convention doesn’t correspond with the provisions over reservations in the Vienna Convention on the Law of Treaties, 1969 and thus recognize those reservations as “legal hybrids”.Conclusions.The structure of reservations to the International Tax Convention is deter-mined by the nature of double taxation agreements. The model lawmaking principle (the use of the OECD Model Tax Convention) allowed developing “umbrella” architecture of relationships between the provisions of the Multilateral Tax Convention and the norms of double taxation agreements. The article categorizes types of reservations as reservations of general nature and treaty-specific reservations. The article also considers the specific properties of reservations made in relation to the provisions of the Convention, which com-pose a minimal standard.