The importance of Siberian forests is evident. In a planetary scale, they play a very significant role in maintaining the Earth's climate and atmospheric gas balances. In a regional scale, forests regulate water and permafrost regimes. Siberian forests are habitats for a wide range of animals and plants, many of them are rare and/or endemic. From the economic point of view, they are a large source for the production of timber and non-wood products. This paper deals with the ecological status of Siberian forests as influenced by both natural and anthropogenic factors. The task of the work is to represent a general estimation of forest decline, to describe the major reasons and tendencies. The influence of industrial pollution is treated in a more detailed manner. For the analyses, several sources of data were used. The main source was data delivered to IIASA's Siberian Forest Study by the Russian State Committee for Statistics ( Roskomstat or former Goskomstat). The main subjects of this large-scale analysis are the administrative units of Russia – independent republics within Russia, krays and oblasts. For the more detailed studies, administrative units have been divided into so-called ecological regions, or ecoregions, based on natural conditions.