Synthesis of ammonia from the elements (N2+3H2→2NH3) is performed over promoted iron catalysts at high pressures and temperatures (Haber–Bosch process) and represents, for about seventy years, one of the most important industrial catalytic reactions. This report is intended to demonstrate what kind of information on the nature of the catalyst surface, as well as on the microscopic reaction steps, can be obtained by the ‘‘surface science approach’’, i.e., by using a variety of surface spectroscopic techniques and by performing model studies with single crystal surfaces.