<p>The monograph provides experience in classifying and hydrological zoning Soviet rivers based on their hydrological characteristics. The application of geographical zonal laws to the study of river hydrological conditions that are inseparable from the geographical environment made it possible to formulate a genetic classification of rivers, and on this basis, the zonal hydrological zoning of the territory of the Soviet Union was realized. The book is divided into four parts. The first part discusses the basic prerequisites for hydrological zoning, the second part expounds the principles of river classification, the third part expounds the principles of hydrological zoning, and the fourth part describes the hydrological characteristics of each district in the plain and mountainous areas of the Soviet Union. The book contains general and basic characteristics of the causes of hydrological conditions of major medium-sized rivers in the Soviet Union, and points out the water balance factors and the changing laws of river hydrological conditions according to the divided hydrological zones and hydrological zones. This book is aimed at scientific researchers and engineers engaged in the fields of river water resources utilization, hydrological calculation and forecasting, as well as university teachers and students. </p>