The performance of ground-penetrating radar (GPR) is dependent upon the electrical conductivity of soils. Soils having high electrical conductivity rapidly attenuate radar energy, which restricts penetration depths and severely limits the effectiveness of GPR. Factors influencing the electrical conductivity of soils include the amount and type of salts in solution and the clay content. In 2002, the United States Department of Agriculture-Natural Resources Conservation Service (USDA-NRCS) developed a thematic map showing the relative suitability of soils within comparatively large areas of the United States to GPR applications. The Ground-Penetrating Radar Soil Suitability Map of the Conterminous United States is based on soil attribute data contained in the State Soil Geographic (STATSGO) database. Attribute data used to determine the suitability of soils include taxonomic criteria, clay content, electrical conductivity, sodium absorption ratio, and calcium carbonate content. Based on additional testing, several GPR index values have been revised, and a mineralogy override for low activity clays and attribute data for gypsum have been added. Each soil attribute is rated and assigned a relative value ranging from 1 to 6. For each soil attribute, the most limiting (maximum) layer index value within depths of 1.0 (mineral soils) or 1.25 m (organic soils) is selected to represent the soil. For each soil component within a map unit, the attribute index values are summed. The summation represents the component index value of the soil. For each soil map unit, the dominant component index value is selected as the GPR suitability index. This map can be used to assess the relative appropriateness of GPR for soil investigations within comparatively large areas of the conterminous United States.