Wireless backhaul (WBH) is the part of the radio access network (RAN) that carriers data traffic from the end node (ENs) at the edge to the central concentrator nodes (CNs). The optimal choice for WBH involves the issues such as required network throughput, radio interference cancellation, non line-of-sight (NLOS) support, access technologies, and so on. In this paper, several key considerations for WBH are described, and the WBH solutions are classified into four categories based on the spectrum bands. In addition, a comparative table is given to analyze the commercialized WBH solutions in terms of data rate, bandwidth, modulation types, and so on.