Nodulation and nitrogen fixation in the Leguminosae (Fabaceae) family, classification of rhizobia, and quantification of N2 fixed by different legumes are reviewed. Some promising management options intended to improve N2-fixation by direct selection of rhizobia in soil or by screening and breeding of legumes for increased N2-fixation, are discussed. The effects of pruning, soil phosphorus and pH, available nitrogen, and interactions of nematodes and rhizobia on nodulation and N2-fixation are analysed. The fate of fixed nitrogen can be determined by the recovery efficiency of N and leaching and gaseous N losses.