Mobile Ad-hoc Networks are collection of mobile hosts linked wirelessly with no fixed communications or central supervision. The mobile hosts are self-organized and can be deployed everywhere and at any time. One of the major applications of MANETs is military and disaster recovery. These applications demand for proper communication and coordination among the mobile host. This is achieved with the help of multicasting. Multicasting plays an important role in mobile ad hoc networks. Multicasting is more beneficial than multiple unicast in a bandwidth-constrained ad hoc networks. In this paper we made a comprehensive study on existing multicast routing protocols.