The practice of interpreting international legal norms by national courts is an important part of ensuring their effective implementation on a domestic level. This article examines the approaches taken by courts of foreign countries and the Supreme Court of Russian Federation to the subsequent practice in the application of the treaty as a means of interpreting international treaty norms. The results of the research show that there is a trend among national courts to broaden their understanding of subsequent practice as an authentic means of treaty interpretation. In light of the recent amendments to the Constitution of the Russian Federation, the importance of studying the treaty interpretation has gained new relevance. The article is intended for lawyers, researchers, and anyone interested in contemporary issues related to the law of treaties.