Mobile Ad Hoc Network (MANET) is a collection of multi-hop wireless mobile nodes that communicate with each other without any fixed infrastructure or centralized administration. Wireless links issues, nodes mobility and infrastructureless topologies are the main challenges of MANETs routing protocols. Many parameters need to be taken into consideration when evaluating and analyzing the performance of MANET routing protocols, such as network topology, node density, node speed, and network load. In this thesis, three types of routing protocols, namely: Ad Hoc on Demand Distance Vector routing protocol (AODV), Dynamic Source Routing protocol (DSR), and Optimized Link State Routing protocol (OLSR), are modeled, evaluated and compared to each other. Different performance metrics such as network throughput, packet loss, packet transmission ratio (PTR), packet transmission time delay and protocol overhead are used to study the performance of these routing protocols. Line and grid network topologies are modeled using freeway mobility and Random Waypoint mobility models respectively. Simulations results show that for line network topology with variable node speed and heavy network load, the performance of AODV is better than the other two protocols with respect to packet transmission ratio (PTR); while the AODV protocol overhead is less than that of DSR and OLSR; however for transmission time delay, DSR outperforms AODV and OLSR. In grid network topology, for low network density and heavy network load, the AODV is able to achieve slightly more packet transmission ratio than DSR and OLSR for high node speeds and short pause time; while DSR has lower overhead than AODV and OLSR. In contrast, for high node density, the PTR of AODV outperforms the PTRs of the other two protocols. Moreover, DSR has the lowest overhead value over AODV and OLSR. For transmission time delay, OLSR still has the lowest delay measured, while DSR delay increases over AODV delay for high speed and short pause time. Therefore, under grid network topology it’s preferred to use DSR protocol for low network density and light load. However, AODV protocol shows slightly better performance when the network density and load increase. On the other hand, for the applications that require minimum delay, OLSR protocol is the most suitable choice since it has the lowest delay over the two others. A new routing algorithm is proposed and its performance is evaluated by modifying the operation of AODV routing protocol in order to decrease its overhead and improve its performance. The new algorithm improves the route maintenance mechanism of the original AODV by making the process of rediscovering a new path to the unreachable destination when link breakage occurs, initiated by the last fixed nodes just before the link breakage point. In contrast with the original AODV, in which only the source node is responsible for route maintenance, the improved AODV, when simulated in line network topology, shows lower protocol overhead than the original AODV protocol with various node speeds by 18.8% and packet transmission time delay by 42.1%, which leads to an improvement in routing performance of MANETs in terms of throughput by 36.7 % as compared to the original AODV protocol. OMNET++ version 4.0 is used as a simulation tool to model all the evaluation experiments in this thesis.