The investigation of the Martian cryosphere, by ground-penetrating radar and other electromagnetic techniques, requires accurate knowledge of the electrical properties of the planet's regolith and crust. In similar investigations of frozen ground in Siberia, this problem has been addressed by a technique called Radio Wave Geo-Introscopy (RWGI), which is implemented by examining electromagnetic wave propagation between neighboring boreholes. In this way, temporal and spatial variations in the effective electrical resistivity and dielectric permittivity of the intervening frozen ground can be measured. This paper discusses the main principles of RWGI; the procedures, equipment and measurements needed to implement it; how the data is interpreted; and some applications of this technique to investigations of the terrestrial cryolithozone.