The Ministry of Posts and Telecommunications in Japan organized a committee to study millimeter-wave sensing technologies in 1984. The authors outline some of the test results described in the committee's report and clarify what has to be done to put automotive millimeter-wave sensing technology into practice. They describe three types of radar systems, e.g., FM-continuous wave, 2-D imaging, and pulse Doppler, and present the data measured through the laboratory and road tests. Among these systems the FM-CW system showed good performance on a freeway test and under adverse environmental conditions.<>