In the Haber-Bosch process nitrogen is extracted from the air to form ammonia. This is an important stage in the production of artificial fertilizers and the process won Fritz Haber the 1918 Nobel Prize in Chemistry. Even though the chemical process has been known for a long time, thanks to Ertl’s work we now understand how it functions. The reaction can only take place on a catalytic surface of iron. The surface provides support to enable the atoms in the nitrogen molecules to release their bonds so that they can bind to hydrogen and form am­monia. Ertl has studied the reaction with the help of several different spectroscopic methods and put the different results together to form the complete picture.