Research on wireless power transmission by a rectenna using millimeter waves and subterahertz waves is gaining attention. It is expected that energy harvesters at high frequencies will be developed for use with future 5 G. High-power wireless power supply to various applications will be possible because of miniaturization of the rectenna. As described herein, we investigate earlier studies of millimeter-wave wireless power supply, selecting and explaining salient examples of millimeter-wave high power wireless power supply.