This paper instructs about Wireless Underground Sensor Networks (WUSNs) which constitute one of the promising application areas of the recently developed wireless sensor networking techniques. WUSN is a specialized kind of WSN that mainly focuses on the use of sensors at the subsurface region of the soil. This region has been used to bury sensors, usually targeting irrigation and environment monitoring applications, although without wireless communication capability; WUSNs promise to fill this gap and to provide the infrastructure for novel applications. The main difference between WUSNs and the terrestrial WSNs is the communication medium. This project presents advanced channel models that were developed to characterize the underground wireless channel considering the characteristics of the propagation of EM waves in soil and their relation with the frequency of these waves.