The paper presents an overview of the researches on the effects of symbiotic and non-symbiotic nitrogen fixation in natural forests and agroforestry systems. The first studies about potential application of nitrogen fixing microorganisms in plant production were related to agriculture, while the first documented attempt of applying of nitrogen fixation in forestry, is relating to 1894. The results of numerous studies indicate to important role of nitrogen fixation in natural stands, plantations and agroforestry systems, where it is proven that nitrogen, provided to plants by nitrogen fixation, besides for having a positive effect on the vigor of growth, stand productivity and form of trees, has positive effect on the soil properties, as well. The researches analyzed in the paper were performed on different tree species and habitat types, which is significant considering that the forest ecosystems of Serbia are divers both in tree species and habitat characteristics.