Nitrogen is essential for all life. But even though nitrogen makes up 78% of the atmosphere, it's in a form that can't be used by living organisms. Instead it's tied up in nitrogen molecules made up of two nitrogen atoms that share a strong triple bond that's not easily broken. A century ago, two German chemists, Fritz Haber and Carl Bosch, figured out how to sever those bonds with high pressures and temperatures and weld nitrogen atoms with hydrogens to make ammonia, thereby converting nitrogen into the starting material for a nitrogen-rich fertilizer that can be taken up and used by microbes, plants, and people. That process has been so successful that ammonia-based fertilizers now enable farmers to feed billions more people than our planet could otherwise support. But ammonia production also comes at a high environmental cost, as it is responsible for 2% of worldwide energy use and thus a massive greenhouse gas footprint. However, on page 637 of this issue, U.S. chemists report that they've come up with a way to synthesize ammonia from air, water, and sunlight. If the approach can be scaled up, it could offer a means for making an essential commodity without a major cost to the climate.