The availability of nitrogen is one of the major limiting factors to crop growth. In the developed world, farmers use unsustainable levels of inorganic fertilisers to promote crop production. In contrast, in the developing world inorganic fertilisers are often not available and small-holder farmers suffer the resultant poor yields. Finding alternatives to inorganic fertilisers is critical for sustainable and secure food production. Bacteria and Archaea have evolved the capability to fix atmospheric nitrogen to ammonia, a form readily usable in biological processes. This capability presents an opportunity to improve the nutrition of crop plants, through the introduction into cereal crops of either the nitrogen fixing bacteria or the nitrogenase enzyme responsible for nitrogen fixation. While both approaches are challenging, recent advances have laid the groundwork to initiate these biotechnological solutions to the nitrogen problem.