Mobile ad hoc network (MANET) is a special type of wireless network in which a collection of wireless mobile devices (called also nodes) dynamically forming a temporary network without the need of any pre-existing network infrastructure or centralized administration. Currently, Mobile ad hoc networks (MANETs) play a significant role in university campus, advertisement, emergency response, disaster recovery, military use in battle fields, disaster management scenarios, in virtual classrooms, in emergency search and rescue operations, data acquisition in hostile environments, communications set up in exhibitions, conferences and meetings, in sensor network, extension of cellular networks, at airport terminals for workers to share files and so on. In MANETs, there is no pre-established infrastructure to facilitate the routing activity and hence communication between mobile nodes can be achieved through the mobile nodes using multi hop wireless technique. However, wireless devices in ad hoc networks are typically limited power with limited life span. Thus, energy efficiency is a critical issue for battery-powered mobile devices in ad hoc networks. This is due to the fact that failure of node or link allows re-routing and establishing a new path from source to destination which creates extra energy consumption of nodes and sparse network connectivity, leading to a more likelihood occurrences of network partition. Routing based on energy related parameters is one of the important solutions to extend the lifetime of the node and reduce energy consumption of the network. In this dissertation, we evaluated energy efficiency of an existing routing protocols of MANETs based on energy efficient metrics and designed a novel energy aware routing protocols called Balanced Battery Usage routing (BBU in short) and Gossip based Balanced Battery Usage routing (GBBU in short) which uses residual energy, hop count and node density as a cost ii metric to minimize energy consumption, maximize network lifetime and distribute usage of energy among mobile nodes of MANET. The new protocols, which are referred to BBU and GBBU, are simulated using Network Simulator-2.35 and comparisons are made to analyze its performance based on network lifetime, delivery ratio, normalized routing overhead, average collision rate, normalized energy consumption, standard deviation of residual energy of all nodes and average end to end delay for different network scenarios. The simulation results reveal that the proposed energy aware routing protocols make the network active for longer interval of time once it is established by minimizing energy and distributing energy consumption across mobile nodes on the network at the trade off a small amount of end to end delay. For instance, the simulation results of BBU showed an average improvement of 9.15% and 6.83% in network lifetime compared to ad hoc On-Demand Distance Vector protocol (AODV) and Alternate Link Maximum Energy Level AODV (ALMEL-AODV) respectively. Furthermore, a 15.77% and 11.4% reduction of standard deviation of residual energy of all Nodes is also achieved in BBU compared to AODV and ALMEL-AODV. However, BBU increased end to end delay by a 5.75% compared to standard AODV but still achieved a 4.85% better performance compared to ALMEL-AODV. A further extension of the approach using gossiping technique (GBBU) leds to an average improvement in normalized energy consumption by 12.36% and 6.39% under various network density, 13.34% and 9.16% under different traffic loads, 10% and 6.23% under different mobility at the trade off an increase in end to end delay by 6.07% and 2.55% under various network density, 3.94% and 4.19% under different mobility compared to AODV and GOSSIP routing protocols.