Microwave power transmission technology, which is a sub-discipline of the wireless power transmission technology, aims to transmit electrical power without using wires/cables in the microwave frequency band. The retro-reflective beamforming technique has the potential to enable efficient and safe microwave power transmission, as it includes the following two technical elements. First, a directional microwave beam is generated as the carrier of wireless power. Second, the microwave power beam could be steered in real time toward mobile wireless power receiver(s). This book offers a comprehensive narrative of retro-reflective beamforming in the context of microwave power transmission. The book begins with an overview of wireless power transmission technology, microwave power transmission technology, and retro-reflective beamforming technique in its first chapter. Chapters 2 and 3 of the book provide in-depth descriptions of the theory and practical implementation of the retro-reflective beamforming technique for microwave power transmission. Commercial products of microwave power transmission are envisioned to emerge in three practical applications, including internet of things, space solar power, and wireless charging in fully-enclosed space. Chapters 4, 5, and 6 of the book discuss applying the retro-reflective beamforming technique to accomplish efficient microwave power transmission in these three practical applications, respectively. Abundant numerical and experimental examples are provided throughout the book. Retro-reflective Beamforming Technique for Microwave Power Transmission is a valuable resource for the wireless power transmission community. It will be of particular interest to engineers and researchers in the fields of electromagnetics, antennas, and microwave engineering.