As mentioned earlier, underwater network is quite different from the terrestrial networks. The routing protocols for terrestrial networks are broadly divided into two categories: proactive and reactive . In proactive protocols-like OLSR (Optimized Link State Routing)  and DSDV (Dynamic Destination Sequenced Distance-Vector) -nodes periodically share their routing table information with each other, routes are established evenly irrespective of their requirement. This would cause extra overhead especially in higher lossy underwater links. Whereas in reactive protocols, like AODV (Ad-hoc On Demand Distance Vector) , its variants like MRAODV (Multiple Route AODV)  and DSR (Dynamic Source Routing) ; routes are established on demand initiated from the source. In underwater networks, this route establishing mechanism would be time consuming and causes larger delay due to low propagation speed of acoustic signals. So these protocols are no longer feasible to work in harsh underwater environment . There have been many proposed protocols for routing in underwater scenarios . These protocols roughly fall into following two categories. Different aspects of these protocols are given in details.