With the ability to control the wireless environment, intelligent surfaces offer the potential for increased channel capacity, new solutions towards encoding information, and more efficient use of radio waves among many additional capabilities. Intelligent reflecting surfaces, a classification for intelligent surfaces that strictly reflect signals, are planar devices consisting of an array of reconfigurable, reflecting unit cells. This reconfigurable property allows for the manipulation of incoming wireless signals, leading to an adaptable and flexible propagation environment. With increased data traffic and the need to support a large number of users, IRSs and other classes of reconfigurable surfaces adapt the wireless environment to help meet these growing demands. Moreover, the low-power and low-cost nature of IRSs make them easily deployable into current wireless systems to help increase the spectral efficiency of the wireless link.