The Food and Agriculture Organization of the United Nations (FAO) developed a supra-national classification, which offers useful generalizations about pedogenesis in relation to the interactions between the main soil-forming factors.
It was first published in form of the UNESCO Soil Map of the World (1974) (scale 1 : 5 M.).
Originally developed as a legend to the Soil Map of the World, the classification was applied by United Nations sponsored projects.
The FAO soil map was a very simple classification system with units very broad, but was the first truly international system, and most soils could be accommodated on the basis of their field descriptions.
In 1998 this system was replaced by the World Reference Base for Soil Resources.