Function of boundary rivers in hydropolitics cooperation:Danube river study

International rivers, as borders or crossing national borders, have been considered as a significant part of international relations. Especially, approximately half of the worldchr('39')s population lives within the basin of these rivers, and more than 90% are living in countries with these basins. This condition, by creating an undeniable relationship of interdependence, has made water a critical issue for these countries. Thus, as populations and economies grow and develop and national water resources are exploited for additional growth and development, government action and reaction to a higher share of these transnational sources will increase. By the way, the type of government interaction in line with exploiting these common resources includes a wide range of cooperation to tension and war. In some parts of the world, common water resources in the form of rivers have used as a linking factor between nations and governments. So that, instead of conflict, the beneficiary countries take the path of cooperation and convergence and they have taken important steps with regard to the development of the region as optimal management of common water resources. Although the achievement of international cooperation is a long, lengthy and complex path, always, there are many ways to follow, many steps to take, and many options for appraisal and selection. The current research is a descriptive-analytical research and by means of library resources and examining the practical status of cooperation in a part of the Danube River as a model, concluded that cooperation was not just for water agreements and factors such as environmental concerns, regional security, regional benefits (such as joining organizations and ::union::s), mediation (governments, international organizations, and institutions), etc., are effective in this process.