​As the geotechnical engineering profession moves forward into the twenty-first century, the role of seismic testing, as well as other geophysical testing methods, will increase. Geophysical methods present unique advantages, including a strong theoretical basis, the ability to perform the same basic measurement in the laboratory and field, and the noninvasive nature of many of the tests. A brief review of the fundamental concepts of seismic wave testing as applied in geotechnical engineering is presented. Determination of engineering design information (subsurface conditions and design parameters) is illustrated through case histories, which also highlight some of the strengths and inherent limitations of the methods. Suggestions for future directions, applications and potential developments are offered.