In international law treaty interpretation ranks high and plays a key role in ensuring stability and justice in international relations. However, it should be noted that this process is one of the most challenging and contentious tasks, as evidenced by the practice of international courts. Commonly when there is a dispute between two or more states regarding the application of an international treaty, it is because these states have different interpretations of the provisions in question. Likewise, judges often disagree on matters of interpretation, leading to the prevalence of dissenting opinions in the international judiciary system.

The purpose of this article is to examine to what extent the practice of the ICJ demonstrates a special understanding of the rules set out in articles 31-33 of the Vienna Convention on the Law of Treaties, the sources it relies upon when applying these rules, whether it applies other principles of interpretation not explicitly provided for in these articles. The objectives of the article are twofold: to summarize the PCIJ and ICJ approaches to treaty interpretation and to examine how these approaches have evolved over time. An understanding of the complex process of judicial interpretation, which can diverge from or develop the Vienna rules of interpretation, complements recent domestic scientific researches, in which treaty interpretation is considered from a more practical perspective.