The protection and rational use of land and water resources are of fundamental importance for human existence on Earth. Among the principal tasks for the economic and social development of the Soviet Union set forth by the 27th Congress of the Communist Party of the Soviet Union were the strengthening of the protection of nature, mineral resources, the atmosphere, water bodies, flora, and fauna, as well as ensuring the rational utilization and renewal of natural resources. An important component of achieving this objective is the development of measures to regulate water-induced erosion processes and to protect soils from erosion. The development of erosion is associated with the combined effects of a number of natural and anthropogenic factors, including slope length and steepness, watershed size, soil resistance to erosion, the intensity and frequency of heavy rainfall, improper land-use planning, and incorrect cultivation and irrigation practices. Under present conditions, when agricultural production must be expanded through the development of mountainous and foothill regions, the study and development of new and promising methods for preventing soil erosion have acquired particular significance. Mountain landscapes are characterized by strongly dissected terrain, numerous slopes, highly variable precipitation conditions, large volumes of surface runoff, intense manifestations of various forms of soil erosion, and the formation of destructive debris flows within mountain river basins. In Kazakhstan, the problem of preventing water erosion of soils has not yet been sufficiently studied. At the same time, approximately 9 million hectares of potentially cultivable land in the foothill and mountainous regions of southern and southeastern Kazakhstan are threatened by washout and erosion. Although the general patterns governing surface runoff and erosion development have been identified, there remains an insufficient understanding of the characteristics and regularities of erosion processes, and comprehensive systems of anti-erosion measures have yet to be adequately developed. To address the tasks involved in studying erosion processes within this exceptionally complex and highly contrasting natural environment, we employed methods and approaches drawn from landscape science, geography, hydrology, forest-soil amelioration, and soil science. This work examines the problem of erosion and its geographical regionality in the Tien Shan Mountains of Kazakhstan, a region of great importance to the national economy as both a regulator of water resources and an area for agricultural development. The book describes the patterns of surface runoff and soil erosion development under mountain terrain conditions, the characteristics of channel runoff formation and soil loss from small catchments, and provides a scientific basis together with practical recommendations for increasing the effectiveness of anti-erosion forest-reclamation measures and other land-improvement techniques.