This study is based on the concepts of morphotectonics and morphosculpture, which seek to reveal the connections and relationships between modern drainage networks and tectonic as well as morphotectonic structures. The morphotectonic analysis of the river network of the Soviet Union represents the first attempt in Soviet science to conduct a comprehensive study of its structure and genesis. Comparable investigations of such a vast territory have not been described in the world literature. The monograph examines the structural characteristics of drainage networks, the particular features and regularities of their structure and development, their overall patterns, types, channel characteristics, and valley morphology. Special attention is devoted to the relationships between river networks and geological as well as morphotectonic structures, with emphasis placed on the important role of faults and tectonic fractures in these processes. The major stages in the development of river networks and the history of sediment accumulation are identified and distinguished. For the first time, based on the principles of historical paleogeography and morphotectonic analysis, the formation characteristics of the largest trunk river systems of the Soviet Union are described, and the relationship between the stability of drainage networks and the nature and age of geological and morphotectonic structures is clarified. Numerous geomorphologists participated in the preparation of this monograph. They drew upon many years of field observations, published sources, cartographic materials, and aerial and space imagery. The geological and geomorphological heterogeneity of the Soviet territory, together with the diversity of river-network types, made it possible to provide a relatively comprehensive explanation of the relationships between river networks and morphotectonic structures. Approximately three million rivers are found within the Soviet Union. Of these, about 4,000 are classified as medium-sized rivers (100–500 km in length), while 260 are large rivers (more than 500 km in length). The total length of all rivers exceeds 9.5 million km, including about 230,000 km of large rivers and about 670,000 km of medium-sized rivers. The largest Soviet rivers, the Lena, Yenisei, Ob, and Amur, rank among the great rivers of the world. The overwhelming majority of Soviet rivers belong to the Arctic Ocean basin, which occupies more than half of the territory of the Soviet Union. The Atlantic and Pacific Ocean basins together account for less than one quarter of the country's area. An approximately equal area belongs to internal drainage basins, including the hydrological networks of the Volga, Ural, Amu Darya, and Syr Darya rivers. The enormous diversity of natural, geological, and geomorphological conditions within the Soviet Union has resulted in river systems that are heterogeneous not only between drainage basins but also within individual basins themselves. For example, within the Arctic Ocean basin, the eastern (Asian) sector, which is predominantly mountainous, differs sharply from the western sector, which is characterized mainly by lowland plains. In the eastern part of the basin, rivers are abundant in water, contain numerous rapids, flow through narrow and deeply incised valleys that often take the form of gorges, and exhibit signs of relative youthfulness against the backdrop of ancient landscapes. In contrast, rivers in the western sector are characterized by slow currents and broad, often box-shaped, and relatively shallow valleys. Within the Pacific Ocean basin, rivers are predominantly mountainous in character. With the exception of the Amur and Anadyr rivers, they are generally small streams with swift currents, rocky channels, and narrow, incompletely developed valleys, reflecting their overall youthful appearance. In the Atlantic basin, by contrast, the structure of the river network is highly diverse. Rivers in the southern part of the basin associated with the Black Sea and Sea of Azov catchments (except those of the Caucasus) belong to the lowland type and are characterized by gentle gradients, tranquil flow, well-developed valleys, and long histories of development. Conversely, the river network of the Baltic basin displays pronounced youthful features. Many river channels contain shoals, valleys are only weakly developed, and lakes are abundant within the catchments. Additional evidence is provided by the still incompletely established character of modern watersheds relative to rivers draining toward the Black Sea, as well as signs of repeated recent reorganizations of the drainage network. The distribution of river networks across the Soviet Union is highly uneven. This depends on numerous factors, including regional humidity, the lithology and permeability of bedrock, and topographic elevation. In the European part of the Soviet Union, the highest drainage density occurs in the Caucasus, reaching the national maximum of 2.03 km/km² in the upper Terek River basin, and nearly 2.0 km/km² in the upper Tisza River basin of the Carpathians. The lowest drainage densities occur in the arid regions of Crimea and on the eastern coast of the Caspian Sea, where values are below 0.1 km/km². The distribution of river networks in the Asian part of the Soviet Union is even more uneven. Drainage density declines to virtually zero in the deserts of Central Asia, while increasing to 1.5–1.8 km/km² in the mountains of the Tien Shan and Dzungarian Alatau. In Eastern Siberia and Transbaikalia, the lowest densities are found in central Yakutia (0.15 km/km²) and the upper reaches of the Argun River (0.18 km/km²). In northeastern Siberia, Kamchatka, and the mountainous regions of the Far East, where mountain catchments predominate, drainage density ranges from 0.8 to 1.0 km/km². The average drainage density across the Soviet Union is 0.45 km/km². The great diversity of river-system types and their combinations within the Soviet Union makes it possible to understand their distributional structure and to identify important characteristics and regularities of their development. The monograph contains chapters devoted to methods of river-network analysis, their regional characteristics, and several general theoretical and practical issues. In the methodological section, methods for analyzing the overall pattern of drainage networks are reviewed, with particular attention given to the analysis of river longitudinal profiles, valleys, and terraces. A special chapter discusses the application of satellite imagery to morphotectonic analysis of river networks. Throughout the work, the methods are critically evaluated, and their advantages, disadvantages, applications, and limitations are identified. In the regional section, drainage networks are examined according to the major chronotectonic-geomorphological and morphotectonic regions traditionally used in the subdivision of the Soviet territory. In the chapters devoted to selected theoretical and practical issues, the relationships between river networks, tectonic structures, and morphotectonic features are traced, and their significance for petroleum and natural-gas exploration, mineral prospecting and prediction, and solutions to regional engineering-development problems is demonstrated. In addition to researchers from the Institute of Geography of the Academy of Sciences of the USSR, contributors to this monograph included specialists from the Institute of Geology of the Academy of Sciences of the USSR, the Far Eastern Scientific Center of the Academy of Sciences of the USSR, the Academy of Sciences of Ukraine, the Academy of Sciences of Kazakhstan, Moscow State University, the Ministry of Geology and Mineral Resources Protection of the USSR, and the Hydroproject Institute.