The carbon balance of northern mid-latitude terrestrial ecosystems is uncertain, yet important for predicting future rates of CO2 increase in the atmosphere. Analyses based on atmospheric data and models show a net terrestrial sink that ranges between 3.5 and 0.7 PgC/yr in northern mid-latitudes (Tans et al. 1990 Ciais et al. 1995 Rayner et al. 1999 Bousquet et al. 1999a,b, 2000). Analyses based on forest inventories are lower but also variable, especially for Russia and the former Soviet Union, where estimates of carbon balance range between a source of 0.5 PgC/yr and a sink of 1.02 PgC/yr (review of 15 studies by Shvidenko et al. 1996). As Russia represents the largest political unit in the northern hemisphere and contains the largest stocks of terrestrial carbon (Apps et al. 1993, Dixon et al. 1994), it is important to determine the current carbon storage and the net flux of carbon for this country. We propose to determine the current distribution of carbon storage in Russia and changes in that storage over the last decades with an approach that integrates forest inventory data, results of ecological studies, agricultural and forestry data on land-use change, and a combination of Landsat and MODIS data and products. The forest inventory system in Russia has collected consistent and detailed stand level information on millions of hectares annually over the last decades. The large variation in carbon budgets based on these inventory data results from the manner in which the primary inventory data (data from individual stands) are aggregated for regional and country-wide estimates. We shall not use the aggregated totals but, rather, the primary stand data to calibrate Landsat TM scenes in 15 locations throughout the country. We will scale-up these Landsat classifications to the entire Russian territory with MODIS data, and use the coverage to determine the current rates of disturbance, based on the areas of disturbed forests (for example, clear-cut or burned) and rates of regeneration in each ecosystem We will also determine rates of land-use change for the period 1950 to 2000 with tabular data from Russian agricultural and forestry statistics and determine from forest inventory data and the ecological literature the average biomass and rates of growth and decay following disturbance of the major ecosystems of Russia. Finally, we will calculate with a dynamic bookkeeping model (Houghton et al. 1999) the annual flux of carbon between Russia and the atmosphere as a result of changes in land use and fire over the last decades. The proposed work addresses one of the priority issues of the USGCRP and a research area of the NASA ESE program for 2001 and beyond: Carbon Cycle Science. The work will identify, characterize and quantify sources and sinks for carbon (current and past) for a very large and important region of the world.