Introduction Ground-penetrating radar (GPR) is a relatively young geophysical technique. First uses appeared in the 1960s with radio echo sounding of glaciers and ice sheets (Bailey et al., 1964) followed by permafrost analysis (Annan and Davis, 1976). Applications spread with major changes commencing in the 1990s. The history of GPR is intertwined with the diverse applications of the technique. GPR has the most extensive set of applications of any geophysical technique leading to a wide range of spatial scales and concomitant diversity of instrument configurations. A chronological history can be found in Annan (2002). The accompanying references provide further insight into the technology evolution.