This new global system for delineation and codification of the Earth's river basins is a natural system, defined by topographic control of drainage and the topology of the resulting network of rivers. It has been implemented by the USGS using Geographic Information System (GIS) techniques to the North American portions of the GTOPO30 DEMs. The identification numbers which are generated carry valuable topological information which can be easily exploited by standard data base management operations, facilitating analyses of sustainability of natural systems and human activities which intervene or are dependent upon the availability of surface water resources. The topological information of the identification numbers makes full and efficient use of all digits; a series of single five-digit codes is sufficient to uniquely identify subbasins smaller than 4,000 km2 in mean surface area for the North American continent.