Abstract: Wireless sensor networks are enabling applications that previously were not practical. As new standards based networks are released and low power systems are continually developed, we will start to see the widespread deployment of wireless sensor networks in future. One of the pioneering aspects of WSNs is to provide reliable and efficient routing protocols as the networks cannot afford to waste energy at any cost and in addition to energy conservation life time of the nodes is also of primary concern. In this paper energy efficient routing protocols have been divided into four categories: Network Structure, Communication Model, Topology Based and Reliable Routing.

Keywords: Wireless Sensor Networks, Reliability, Efficiency, Routing Protocols.