A synthesis of ground-based measurements and satellite information is described for estimating the amount of monthly averaged biomass burned in year 2000 with a spatial resolution of 1 ¿ 1 km on a global scale. Emissions of trace gases and aerosols from open biomass burning are estimated from burned areas, fuel load maps, combustion factors, and emission factors. Burned area was quantified by using satellite data in conjunction with a fractional vegetation cover map. To account for spatial heterogeneity in the main types of vegetation within each 1-km grid cell, global fuel load maps have been developed from biomass density data sets for herbaceous and tree-covered land together with global fractional tree and vegetation cover maps. In regions with 40--60% tree cover a relationship between combustion completeness (or combustion factor) in fine fuels and tree cover based on recent field studies is implemented. In regions with 60% tree cover and for coarse fuels in regions with 40--60% tree cover, average values for combustion factors and emission factors from field measurements are used. In addition to biomass burning from open vegetation fires, the emissions from biofuel burning in 2000 are estimated. Our best estimate for the global amount of burned biomass in 2000 is 5613 Tg DM yr-1, of which 2814 Tg DM yr-1 is associated with open burning and the remainder with biofuels. The total emissions are 2290 Tg C yr-1 (as CO2), 496 Tg CO yr-1, 32.2 Tg CH4 yr-1, 38.0 Tg NHMC yr-1, 11.5 Tg HCHO yr-1, 9.2 Tg CH3OH yr-1, 21.7 Tg CH3COOH yr-1, and 38.3 Tg PM2.5 yr-1. Our estimates for CO2, CO, and CH4 emissions from open biomass burning combined with estimates of those from biofuel burning are in the range of the estimates constrained by chemical transport models and measurements. Our use of spatially and temporally explicit data and these comparisons to global models support the conclusion that our source map offers improvements in the emission data sets for estimating the global effects of biomass burning.