Before intelligent decisions involving soil and foundation engineering design can be made on any engineering project, information is necessary on the properties and extent of soils present at the project site. Only when adequate information is available on surface and subsurface conditions can proper consideration be given to the economical design, safety, and probable performance of a project. The art and science of soil engineering have progressed to the point where information obtained solely from shallow boreholes and from tests on samples extracted from such boreholes can no longer be considered as providing adequate design data for the use of soils in engineering projects. By using geologic and pedologic interpretation as well as geophysical and other reconnaissance techniques, detailed information obtained from a few boreholes may be projected over a large area with reasonable confidence. Many exploration methods have been developed and used for years in related disciplines, such as petroleum engineering, and these methods should be recognized and more fully applied to soil exploration. The many methods available for the exploration of soils can be broadly classified as indirect or direct. Under indirect methods are aerial photographic interpretation, pedologic and geologic reconnaissance, and surface and borehole geophysics, all of which would provide useful information on most soil projects. However, data obtained by these methods should be supported by actual field reconnaissance, sampling, and testing.