Nitrogen is one of the key drivers of global agricultural production, with between 150 and 200 million tonnes required each year to produce the world’s food, animal feed and industrial products. Improving the efficiency with which Nitrogen is used in world agriculture is vital to the long-term sustainability of the planet, as gaseous losses contribute to global warming, and leaching and erosion losses to the degradation of watercourses and storages. ACIAR recognised the need for improvements and put out a publication on Methods for evaluating nitrogen fixation by nodulated legumes in the field, in 1989. That practical handbook was widely used, with about 700 copies distributed, more than 100 citations in refereed journals and positive feedback from overseas and Australian scientists. In the 20 years since 1989, significant advances have been made in the development and application of techniques for measuring N2 fixation, prompting the need for this revision of the handbook.