The World Reference Base, or WRB, is a soil classification system that is used as the global standard. It is the result of an international collaboration led by the International Union of Soil Sciences Working Group.
The WRB's classification system includes 32 major soil groups and more than 120 qualifiers for soil characteristics. The 2014 version of WRB includes guidelines for constructing small-scale map legends.
The WRB is an initiative of the United Nation's Food and Agriculture Organization. The FAO published the first World Reference Base for Soil Resources in 1998. The IUSS endorsed the classification system at the 1998 World Congress of Soil Science.