Among the many exogenic factors involved in shaping the Earth's continental surface, the activity of flowing water is of primary importance. Within the fluvial system, rivers occupy a special position. They are the principal arteries of water circulation acting continuously across vast continental areas, regularly transporting enormous quantities of solid material in the form of sediment and dissecting the land surface through networks of river valleys. By cutting down into the land surface, particularly under conditions of tectonic uplift, rivers increase topographic relief and slope gradients, thereby intensifying sheet erosion, promoting the development of primary linear erosional forms, and enhancing various slope processes ranging from the slow downslope movement of weathering products to rapid catastrophic events. The products of weathering and denudation originating on slopes enter rivers from throughout the drainage basin. Therefore, the existence of a river system is possible only when, at every point within it, the flowing water possesses “...such a velocity that it is capable not only of removing along the valley floor the material delivered into the channel by slope runoff, wind, and glaciers, as well as material entering from slopes by slumping, rockfall, and collapse, but also of deepening and clearing away the remains of dead aquatic vegetation accumulated on the valley floor. Otherwise, the river channel would gradually disappear ... as a result of being filled with mineral and plant material...” (Makkaveyev, 1955, p. 45). The transport of solid material within river flow is a complex and multifaceted process whose mechanisms manifest themselves differently in different parts of a river system and under varying combinations of natural conditions. While transporting sediment, which represents not only the products of terrestrial denudation but also material generated by the interaction of flowing water with the riverbed and banks through channel erosion, rivers simultaneously create pools and shoals, meanders, islands, and floodplains. The latter are, on the one hand, accumulations of fluvial sediment (alluvium) that have ceased movement, and on the other hand, the foundation upon which river terraces develop. Today, the study of channel morphology and channel dynamics is one of the branches of geomorphology with the strongest physical basis. The role of rivers in the formation of surface relief was examined in the fundamental work Erosion of River Channels and Their Drainage Basins (1955) by N. I. Makkaveyev. At the same time, the geographical characteristics of channel processes and their relationship with non-zonal factors, which are independent of geographical location and governed instead by the hydraulic laws of channel flow, remain insufficiently understood. Solving this problem would make it possible to establish typical complexes of channel landforms associated with drainage-basin conditions, river dynamics, and valley geomorphology, and would permit a more accurate and scientifically grounded assessment of the role and place of channel processes within the overall system of exogenic geomorphic formation. Understanding the laws governing channel formation is also of great importance for addressing numerous practical problems. Any branch of the national economy that develops within river valleys must, to some degree, take river activity into account, because interference with river dynamics inevitably triggers a chain of processes whose consequences must be anticipated in order to avoid unfavorable outcomes. For example, to ensure the effectiveness of navigation-channel dredging works, it is necessary to make the fullest possible use of the channel-forming activity of the river flow itself. The proper selection of navigation routes and the stability of navigable depths depend largely on the extent to which river-training measures correspond to the actual dynamics of the channel and take account of the specific behavior of channel landforms. In other words, navigation conditions and methods for improving them depend upon the natural conditions of the regions through which rivers flow, since those conditions determine the nature of channel dynamics. Large hydraulic engineering projects require scientifically based forecasts of channel deformations that may occur as a result of human-induced changes in river dynamics. The construction of bridges, water-intake facilities, embankments, and other structures also cannot be undertaken without consideration of channel processes. Planned large-scale water-transfer projects will not only create artificial channels but will also alter the channel-forming activity of natural streams; in both cases, channel processes will develop differently according to local natural conditions. A particularly important application of channel-process theory is found in agriculture, since the most fertile meadow lands are often located on floodplains, and river activity must be considered when developing land-reclamation schemes. The study of river channels and floodplains is also of great significance for analyzing alluvial deposits and for the exploration of placer mineral deposits. Driven by practical needs, river channels have become objects of study for both natural and engineering sciences. This situation has substantially contributed to the development of channel-process theory, because phenomena observed in nature have received rigorous physical explanations, while their direct engineering applications have made it possible to test and refine established principles in practice. At the same time, further progress in the study of river channels as natural objects is possible only when channel processes are not regarded as “...a sequence of phenomena developing in isolation from their geographical environment and without regard for the specific characteristics of the basin landscape” (Makkaveyev, 1955, p. 3). The physical-geographical foundations of channel-process theory were established by N. I. Makkaveyev, who was the first to view the river channel as the lowest link in a complex chain of erosional and depositional processes. This enabled him to conclude that the entire landscape environment of a drainage basin exerts an influence on the channel-forming activity of rivers. The present study is devoted to identifying the characteristics of river-channel forms that develop under different natural conditions, as well as the general and regional features of channel processes. In addition to analyzing physical-geographical, geological, and geomorphological factors and their influence on river channels, particular attention is given to the various channel and floodplain types of both lowland and mountain rivers and to their dynamics. Although the discussion does not attempt complete coverage of the subject, it nevertheless demonstrates some of the most important features of river channel formation in different regions of the Soviet Union and substantiates the possibility of applying the results of regional channel-process studies to the solution of practical problems. This research is based on materials collected during investigations conducted on the Northern Dvina, Vychegda, Ob, Amu, Biya, Katun, Lena, Kirenga, Taz, Pur, and Yana Rivers, in the estuary of the Indigirka River, and on rivers of the western Transcaucasian mountain and foothill regions. Most of these investigations were related to solving practical national economic problems, especially the preparation of general navigation-development plans and comprehensive measures for improving navigation conditions. Throughout all the years of this research, the author received constant support and guidance from Honored Scientist of the Russian Federation, Doctor of Geographical Sciences, and Professor N. I. Makkaveyev, for which he expresses his sincere and profound gratitude. Colleagues from the Laboratory of Soil Erosion and River Processes of Moscow State University, including K. M. Berkovich, O. A. Borsuk, V. N. Korotayev, R. V. Lodina, B. V. Bely, A. L. Bogomolov, O. M. Kirik, A. A. Zaitsev, S. N. Rulyova, and E. N. Sakharova, participated in the research and processing of materials. A large portion of the data was obtained from the Northern, Ob, Lena, and Irtysh Basin Waterway Administrations of the Ministry of River Transport of the Russian Federation, whose support provided extensive opportunities for conducting research on major lowland rivers. The author also expresses deep gratitude to all colleagues who participated in the work, as well as to M. M. Bezdenezhnevsky, N. S. Lyubimov, E. M. Pasekevich, and other personnel of the basin administrations for their continuous assistance in carrying out these studies.