Towards Cooperative Routing in Underwater and Body Area Wireless Sensor Networks Wireless Sensor Networks (WSNs), particularly Wireless Body Area Networks (WBANs) and Underwater Wireless Sensor Networks (UWSNs) are important building blocks of upcoming generation networks. Sensor networks consist of less expensive nodes having the features of wireless connectivity, very less transmission power, limited battery capacity and resource constraints. Due to low cost and small size, sensor nodes allow very big networks to be installed at a viable price and develop a link between information systems and the real globe. Cooperative routing exploits the transmission behavior of wireless medium and communicates cooperatively by means of neighboring nodes acting as relays. Prospective relays as well as the destination nodes are chosen from a set of near-by sensors that use distance and Signal-to-Noise Ratio (SNR) of the link conditions as cost functions { this contributes to signi cant reduction in path-loss and enhanced reliability. In this dissertation, we propose three schemes Link Aware and Energy Efficient protocol for wireless Body Area networks (LAEEBA), Incremental relay-based Cooperative Critical data transmission in Emergency for Static wireless BANs (InCo-CEStat) and Cooperative Link Aware and Energy Efficient protocol for wireless Body Area networks (Co-LAEEBA). These protocols are efficient in terms of link-losses, reliability and throughput. Consideration of residual energy balances load among sensors, and separation and SNR considerations entrusts reliable data delivery. As a promising technique to mitigate the effect of fading cooperative routing is introduced in the functionality of LAEEBA and Co-LAEEBA protocols. Similarly, incremental relaying in InCo-CEStat account for reliability. Simulation results show that our newly proposed schemes maximize the network stability period and network life-time in comparison to other existing schemes for WBANs. In Underwater Acoustic Sensor Networks, demand of time-critical applications ix leads to the requirement of delay-sensitive protocols. In this regard, this disserta- tion presentsve routing protocols for UWSNs; Cooperative routing protocol for Underwater Wireless Sensor Networks (Co-UWSN), Cooperative Energy-Efficient model for Underwater Wireless Sensor Networks (Co-EEUWSN), Analytical ap- proach towards Reliability with Cooperation for Underwater sensor Networks (AR- CUN), Reliability and Adaptive Cooperation for Efficient UWSNs (RACE) and Stochastic Performance Analysis with Reliability and COoperation for UWSNs (SPARCO). In these protocols, physical layer''s cooperative routing is explored for the design of network layer routing schemes that prove to be energy-efficient as well as path-loss aware. The concentration is focused on Amplify-and-Forward (AF) scheme at the relay nodes and Fixed Ratio Combining (FRC) technique at the destination nodes. Nodes cooperatively forward their transmissions taking bene t of spatial diversity to reduce energy consumption. Simulations are conducted to validate the performance of our proposed schemes in comparison to the selected existing ones. Results demonstrate the validity of our propositions in terms of selected performance metrics.