Nitrogen fixation is the process by which nitrogen gas (N2) is converted into ammonia (NH3). This process is essential for life on Earth because nitrogen is a key component of proteins, nucleic acids, and other important molecules. Nitrogen fixation is carried out by bacteria and archaea that have the enzyme nitrogenase. Nitrogenase catalyzes the reduction of N2 to NH3 using ATP as the energy source.

The Haber process is an industrial process that converts nitrogen gas and hydrogen gas into ammonia. The Haber process is used to produce fertilizer for crops.