With the development of sensing networks and Internet of things, wireless sensor networks have been applied to different fields of our society. With the perceived sensing demands for soil, mining lanes, etc., wireless underground sensor networks (WUSNs) have developed rapidly recently. Compared to typical terrestrial wireless sensor networks, WUSNs have unique applications and features due to their wireless transmission characteristics and layout environments, especially WUSNs in soil. In this paper, we discuss the wireless propagation characteristics and engineering implementation methods of WUSNs in tunnels/tubes/pipelines/lanes and WUSNs in soil. The prospects for the future development of WUSN are discussed as well.