The atmosphere is largely composed of nitrogen gas in a form that is mostly chemically and biologically inert.  In pre-industrial times, the nitrogen contribution from recycling organic matter and legume rotations for food production had largely reached its limits.  The global reserves of naturally occurring guano and sodium nitrate were rather small and rapidly exploited.  Nineteenth century scientists in Europe and North America were concerned about impending food shortages due to lack of sufficient nitrogen to sustain crop growth. Fritz Haber discovered the technique for synthesizing ammonia and Carl Bosch developed the ammonia production process suitable for an industrial scale.  It is estimated that nearly half of the global food supply is currently supported by nitrogen fertilizer.  The evolution of the modern nitrogen fertilizer industry since the 1950’s will be described, beginning with ammonia synthesis and its subsequent conversion to other common solid and fluid fertilizers.  Global production and transportation of nitrogen fertilizer will be highlighted.