Nitrogen is generally the first limiting nutrient for plant growth. Until the invention of synthetic nitrogen fertiliser, early in the 20th century, legumes, with their capacity for biological nitrogen fixation (BNF) in symbiosis with bacteria of the Rhizobiaceae, were the main source of agricultural nitrogen. As nitrogen fertiliser became cheap, its use expanded and has continued to grow, with the result that there is now considered to be too much reactive N in the biosphere, with associated problems of nitrate leaching into water and nitrous oxide emission into the atmosphere. Legume crops offer a great deal more to agricultural systems than BNF alone, and the Legume Futures project has explored many of these effects. This report presents a synthesis of the effects of agricultural legumes in rotations. It refers to other Legume Futures reports, in preparation at the same time, for greater depth on some issues.