The article examines unilateral acts of states in the international legal system based on a complex systemic analysis. The methodological basis was the dialectical method, which made it possible to understand the essence of international legal obligations of states in inseparable unity and general connection. The relevance of the study is determined by the trends inherent in modern international law. First, with the development of information technologies, and especially with the development of forms of information transmission, the sphere of activity of states is transformed. An increasing number of interested persons knows their positions on a wide range of international legal issues. On the one hand, it simplifies the process of identifying the state’s position when its analysis is necessary for international legal qualification. On the other hand, in such a situation, the possibilities for interpreting the behavior of a specific state from the point of view of its agreement or disagreement with a certain legal situation expand. In the practice of international relations, there is an expansion of the system of sources of international law. The study of these sources is necessary for understanding the foundations of international law, solving specific international problems and increasing the effectiveness of international cooperation. As the practice of international jurisdictional bodies accumulated, the subject of study of which was unilateral acts of states, the research emphasis shifted from establishing the essence of unilateral acts to assessing their relationship with the sources of international law. It is noted that unilateral acts play an important independent role in the modern international system, which is characterized by both fragmentation and growing globalization. Modern means of communication have made it possible to make unilateral acts one of the most frequently used tools of state interaction. The appropriateness and necessity of the development of the legal regime of unilateral acts is emphasized and substantiated. Unilateral acts of states are recognized as independent additional sources of international law capable of generating international legal norms, and they can be found in the «sources» section of many leading international legal documents.