Reflectarray antennas refer to the class of radiating structures that are comprised of an array of radiating elements, reradiating the energy that is impinged on them from one or more radiating feeds that are located in free space. The constituent radiators that build a reflectarray can be shaped to bring about some flexibility in the way that antenna operates such as multiband/polarization operation. The printed nature of these elements allows integration of active elements that can further enhance the functionality of the reflectarray. This allows for capabilities such as power amplification, adaptive beam shaping, and beam switching. This resource presents design guidelines along with details on different types of reflectarrays and methods of analysis. Beginning with introductory material on reflectarray antennas, this book progresses to the presentation of state-of-the-art research in the field. A direct comparison with conventional reflector antennas is provided, focusing on conventional efficiency figures of reflectors. Moreover, this book offers remarks on the future direction of reflectarray research and also potential applications of the technology in face of the emergence of new fabrication techniques to accommodate both passive and active elements.