The Tigris and Euphrates river basin, spanning Turkey, Syria, Iraq, and Iran, is crucial both regionally and globally. Its utilization has become a political and security challenge. The principle of equitable and reasonable utilization, a key tenet of international law, is essential for managing this basin. This research employs a descriptive-analytical approach to explain this principle, identify its conventional and customary sources, and assess the factors affecting its application. It examines the basin's geographical, natural, and environmental conditions to evaluate how the principle is applied. The construction of dams, excessive groundwater use, and extensive irrigation have led to reduced water inflow and severe impacts on agriculture, the environment, and local communities. These issues highlight a weakening commitment to equitable utilization. Urgent cooperation among riparian states is needed to develop a comprehensive plan that ensures fair water use and sustainable ecological preservation for the Tigris and Euphrates basin.

Keywords: International Law of Watercourses, Tigris and Euphrates River Basin, Transboundary Watercourses, Equitable and Reasonable Utilization.