Deep seismiC sounding was proposed by G. A. Gamburtsev and developed under his guid­ ance during the period 1948-1955 at the Institute of Physics of the Earth of the Academy of Sciences of the USSR. During that period also, the first geophysical results concerning the deep structure of the earth's crust in several regions in Tien-Shan, the Pamir, and Turkmenia were observed. Beginning with 1956, the deep seismic sounding method has been used widely by geo­ physical research groups as well as by geophysical service organizations for regional studies in the USSR. Descriptions of this work have been given in reports by Yu. N. Godin, V. V. Fedynskii, D. N. Kazanli, and others. New variants of the deep seismic sounding method have been developed; continuous profiling (Yu. N. Godin, and others), and point soundings (N. N. Puzyrev, and others). Deep seismic soundings have been carried on outside of Russia also, and studies have been carried out on the use of the deep seismic sounding method in marine applications (E. I. Gal'perin, S. M. Zverev, 1. P. Kosminskaya, Yu. P. Neprochnov, and others). OVer the past decade, the deep seismic sounding method has joined the suite of geo­ physical studies as a highly detailed method for studying the earth's crust and upper mantle to depths of 50 to 100 km on land, and of 15 to 25 km in the deep oceans.