The basins of the Ob and Yenisei Rivers occupy vast areas of Western and Eastern Siberia. These rivers possess enormous hydropower resources, and their development has already begun. The Novosibirsk Hydroelectric Power Station has been built on the Ob River, while the Yenisei, one of the largest rivers in the world, has been dammed near Krasnoyarsk, and construction of the Sayan Hydroelectric Power Station has also commenced. The intensive industrial and agricultural development of this region, together with extensive forest harvesting, has created complex challenges for hydrology, and particularly for forest hydrology, requiring investigation of the influence of forests on the hydrological and climatic conditions of these river basins. The hydrological role of forests has already been studied in the European part of the Soviet Union. However, data concerning the influence of Siberian forests on runoff and the factors affecting it remain insufficient. Between 1960 and 1963, the Institute of Forestry and Timber of the Siberian Branch of the USSR Academy of Sciences organized studies on the influence of forests on the principal components of the water balance, namely precipitation, evaporation, and runoff, in different regions of the Ob and Yenisei River basins. Investigations were also conducted into how these components vary with altitude within the mountain taiga zone. The objective of this research was to obtain scientifically substantiated data for long-term planning purposes, including forest restoration, timber harvesting planning, the reassessment of the optimal arrangement of water-protection forest belts along major rivers, the determination of effective afforestation schemes for sparsely forested agricultural regions, the conversion of forest lands to other land-use categories, and the clarification of the influence of forests on the hydrological regimes of rivers and reservoirs. These issues are directly connected with hydraulic engineering development and irrigation projects in Siberia. The findings may serve as a scientific basis for integrated solutions to forestry, hydraulic engineering, and agricultural problems related to the utilization and conservation of water resources. The present work represents the first step toward studying the complex interactions among climate, forests, and runoff under the conditions of Siberia's extremely continental climate. It also includes investigations conducted under the unique mountain taiga conditions of the Sayan Mountains and the Altai Mountains. The author expresses gratitude to R. N. Achikolova for carrying out most of the processing and organization of the collected materials, and also thanks D. L. Sokolovsky and V. V. Rakhmanov for reviewing the manuscript and providing a number of valuable comments and suggestions.