Human activities such as combustion of fossil fuels, intensive agriculture and stockbreeding, have significantly altered the global nitrogen cycle in the last several decades, resulting in increases in the concentrations of nitrogenous compounds in the atmosphere and increases in N deposition several fold. Chronically elevated N deposition to forests can lead to changes in tree growth, mortality, species composition, and to possible decline in soil fertility and drainage water quality. A large number of experiments have been carried out in Europe and Northern America to identify the specific role of N deposition on changes observed in water quality and tree health. Chronically elevated N deposition also affects litter decomposition, a critical processes controlling nutrient cycling, soil humus formation, soil fertility, and primary productivity. Based on available scientific evidence the effects of N deposition on forest litter decomposition are reviewed in this paper. Nitrogen deposition can have indirect and direct effects on forest litter decomposition. By changing the composition of the forest floor and litter chemistry, N deposition indirectly changes litter decomposition rates. The direct effects of N deposition on forest litter decomposition range from positive to negative, and the mechanisms are reviewed in this paper. Finally, present and future research about the effects of N deposition on forest litter decomposition are also discussed.