Abstract: Human activities have greatly accelerated emissions of both CO2 and reactive nitrogen to the atmosphere. Because N availability often limits forest productivity, it has long been expected that anthropogenic N deposition is stimulating forest C sequestration. However, quantitative estimates from models and plot-level studies vary dramatically, and observational evidence has been lacking for deposition-induced stimulation of regional forest growth. The responses of forest soil C storage and solute C loss are even less well-understood. I will present recent work reviewing historical estimates of the importance of N deposition as a mechanism of terrestrial C sequestration, along with new evidence of the effects of N additions on forest growth, soil decomposition, and loss of dissolved organic carbon . We find that N additions have markedly reduced rates of decomposition at 4 of 6 long-term experiments in the Northeast, but that effects on DOC losses across a dozen long-term experiments appear driven more by soil response to acidification than to N itself. Lastly, we find that N deposition has affected tree growth, survival, and C storage across the northeastern and north- central USA during the 1980s and 1990s, with varying consequences for both growth and mortality of different tree species, perhaps due in part to differences in tree mycorrhizal association. Aboveground biomass increment increased by 56 (40-78) kg C per kg N deposition, amounting to a 36 (27-46) % enhancement over pre- industrial conditions. These observations indicate that atmospheric N deposition is a substantial contributor to global C sequestration.