During the past decade, economic development in the vast foothill regions of southeastern Kazakhstan, together with the growth of cities and other settlements and the increase in population, has led to a substantial rise in water consumption. The attention of both practitioners and scientists has increasingly focused on the high mountain regions, where the greater part of the river runoff utilized by the national economy is generated. Even greater scientific and practical interest, however, is directed toward glaciers, which constitute one of the most important components of the hydrological balance during dry periods. At such times, glaciers effectively serve as the sole source of river replenishment during the summer months, when water demand reaches its maximum. During these periods, glacier meltwater fills irrigation systems, brings life to fields, orchards, and vineyards, and ensures the functioning of hydroelectric facilities, industrial enterprises, and water supply systems for both urban and rural areas. Glaciers are also important for transportation and civil engineering in mountainous regions, for the development of forestry and agriculture, and for tourism and mountaineering. The glaciers of the Trans-Ili Alatau occupy an area of 510 square kilometers and number 466 in total, representing approximately 7% and 8%, respectively, of the glacierization of the entire Tien Shan. These glaciers contain about 30 cubic kilometers of ice. Although their scale may appear modest, the glacierization of the Trans-Ili Alatau is not only an important source of runoff formation but also an excellent natural laboratory for studying contemporary glacier evolution, interactions between glaciers and the external environment, internal mass exchange processes, and the future development of moisture conditions in southeastern Kazakhstan and adjacent regions. Glaciers are continually undergoing changes in both their condition and size. The rapid movement of glaciers along valleys, as well as the sudden drainage of lakes dammed by glacier ice or moraines, often triggers landslides, floods, and debris flows, posing a threat to construction and development in both mountain and foothill regions. Variations in glacier runoff caused by changes in glacier conditions are of great importance for irrigation and hydropower development. Modern glacier fluctuations occur against the backdrop of broader environmental changes during the Anthropocene, a period in which glacier dimensions and their variations have reached significant magnitudes. As hydrological objects, glaciers are affected by climatic fluctuations, especially variations in air temperature and moisture conditions, which exert the greatest influence on glacier behavior and determine their external mass and energy exchange. Changes in external mass and energy exchange, in turn, directly affect the internal mass and energy exchange of glaciers. The latter remains comparatively little studied, and only in recent years have the first steps been taken toward investigating this labor-intensive and theoretically complex problem. The history of glacier condition and fluctuation studies contains a wealth of information that retains its scientific value to this day. Nevertheless, a number of modern glaciological problems, especially those concerning the mechanisms of glacier fluctuations, cannot be resolved solely on the basis of these historical data. Long-term classical measurements have provided information on changes in glacier length, area, and volume, as well as fluctuations in flow velocity. In a more limited number of cases, data useful for evaluating glacier mass balance have also been obtained. The results of such investigations serve as a foundation for assessing contemporary glacier development, the relationship between glacierization and climate, trends in regional moisture conditions and river runoff, and the possibility of catastrophic phenomena associated with glacier advance or retreat. Following the completion of observations during the International Geophysical Year (IGY), research in the Trans-Ili Alatau was conducted in accordance with the glacier fluctuation research program developed by the Commission on Snow and Ice of the International Association of Scientific Hydrology. At the same time, within the framework of the “Glacier Fluctuations” project, extensive and demanding inventory work was carried out. Glacier catalogs were compiled for the Trans-Ili Alatau, Kungey Alatau, Terskey Alatau, and the Central Tien Shan within Kazakhstan, and the results were published in individual volumes of the Catalogue of Glaciers of the USSR. In 1965, the glacier fluctuation research and glacier inventory program for representative mountain glacier basins, together with a coordinated program of heat, ice, and water-balance studies, was incorporated into a new international geophysical initiative, the International Hydrological Decade (IHD). The Tuyuksu Mountain Glacier Basin (Fig. 1) was included in the chain of representative basins located near the global mid-latitude belt (approximately 45° N). Various organizational difficulties and shortages of personnel prevented the Department of Geography of the Academy of Sciences of the Kazakh SSR, which directed glaciological investigations in the Trans-Ili Alatau, from beginning observations under the IHD program on time. Nevertheless, before the Department formally commenced work under the program in 1969, extensive integrated studies had already been conducted on the Tuyuksu Glacier, making it possible subsequently to fulfill the IHD program in its entirety. For the Tuyuksu Mountain Glacier Basin, the objectives of the research included investigating the conditions of the Almaty River basin and the components of its hydrological balance; studying runoff fluctuations associated with variations in climatic factors and the heat balance of glacier surfaces; identifying the temporal regularities governing runoff formation; and forecasting future trends in regional moisture conditions for the purposes of water-resource utilization and long-term economic planning. In accordance with the General Program for Work in Representative Mountain Glacier Basins of the USSR, approved by the Interdepartmental Commission of the Soviet IHD on 1 May 1968, the Department of Geography of the Academy of Sciences of the Kazakh SSR developed a detailed research plan. Two principal integrated research programs were established: Glacier-hydroclimatic investigations; Glacier-hydrophysical and structural-petrographic investigations. Each program comprised several interrelated components designed to ensure fulfillment of the stated objectives. The results of observations from all sections of the glacier-hydroclimatic program were published in Observation Data from USSR Mountain Glacier Basins within the International Hydrological Decade [58]. These reports followed the standard format adopted for all mountain glacier basins and included diagrams, charts, tables, methodological explanations, and annual scientific analyses of water, ice, and heat balances. In addition to these reports, the responsible investigators published numerous scientific papers and reports based on IHD observations. In these publications, the results were synthesized and discussed in relation to contemporary thermal conditions, changes in atmospheric moisture, and glacier evolution. The present monograph is based on materials collected during the International Hydrological Decade and adjacent years. These materials include observations and research findings covering all topics specified under the international program and incorporated into the glacier-hydroclimatic research complex. During preparation of the monograph, the authors also made use of data from the Kazakhstan Administration for Hydrometeorology and Environmental Monitoring (Kazakh UGKS), particularly the seven-year series of observations conducted between 1968 and 1974 at the Tuyuksu-2 Glacier Meteorological Station under the IHD heat-balance program. The monograph was prepared under the scientific supervision and editorship of Senior Research Scientist K. G. Makarevich of the Department of Geography of the Academy of Sciences of the Kazakh SSR. The chapters were authored by members of the Trans-Ili Glacier Research Group of the Department of Geography: K. G. Makarevich: “History and Organization of Basin Research,” “The Position of the Tuyuksu Mountain Glacier Basin within the Mountain Natural System,” “Accumulation,” “Ablation of Debris-Covered and Glacier Surfaces” (with E. N. Vilesov), “Glacier Mass Balance and Its Relationship to Meteorological Indicators” (with T. Ya. Denisova and participation of E. N. Vilesov), “Liquid Runoff and Water-Ice Balance of Mountain Glacier Basins,” and “Conclusions.” E. N. Vilesov: “Structure and Morphology of Mountain Glacier Basins and Glaciers,” and “Internal Nourishment of Glaciers and the Firn Zone.” T. Ya. Denisova: “Climatic Conditions for Glacier Existence and Runoff Formation.” R. G. Golovkova: “Heat Balance of Glacier Surfaces During the Ablation Period.” P. F. Shabanov actively participated in the preparation of certain chapters (Chapters 6-10). Technical processing of materials and preparation of the manuscript were carried out by A. K. Makarevich, N. N. Koneva, and T. M. Sokolova. A number of valuable comments and recommendations were provided by A. N. Klenk, Chairman of the IHD Glaciology Section Working Group on Representative Mountain Glacier Basins, N. V. Davidovich of the Glaciology Department of the Institute of Geography of the Academy of Sciences of the USSR, and many other colleagues.