Time Domain Reflectometry (TDR) is a remote sensing electrical measurement technique that has been used for many years to determine the spatial location and nature of various cable faults. In the 1950s TDR technology was adapted to locate and identify faults in power and communication cables. As a result, TDR cable testers are considered standard equipment in these industries. In the 1970s TDR technology began to be applied to geomaterials and has been adapted for use by soil scientists, agricultural engineers, geotechnical engineers and environmental scientists. This article concentrates on the geotechnical application of monitoring subsurface deformation in soil. If there is sufficient interest, future articles in GIN could focus on use of TDR for monitoring moisture content and pore water pressure.