Near-surface geophysics is applied to a broad spectrum of problems, and new application areas continue to arise. The noninvasive tools used to examine near-surface earth materials employ electrical, electromagnetic, or mechanical energy sources, along with passive techniques that measure the physical parameters of the earth. Most advances over the past 75 years have emerged from instrument evolution and computer-processing techniques. Societal needs, such as detecting unexploded ordnance following military operations, have driven research efforts. Other compelling factors, such as the need for potable groundwater, the enactment of laws that have spurred geophysical surveying for archaeological purposes, and the necessity for better soil-physics information in geotechnical engineering and agriculture, are present worldwide.