Ad hoc networking involves multihop, peer-to-peer communication between a group of wireless mobile nodes in a network with a dynamically changing topology. Achieving energy-efficient communication in such a network is more challenging than in cellular net works due to the absence of a centralized access point that can administer power control. For example, the commonly used MAC protocol for ad hoc networks, the IEEE 802.11 MAC protocol, uses a fixed power for all packet transmissions, for reasons of simplicity and to maintain the correct operation of its collision avoidance mechanism. In this thesis, I propose a distributed power-control based MAC protocol for ad hoc networks that uses variable transmission power for the control (RTS, CTS) packets and the minimum required transmission power for the DATA and ACK packets. The proposed solution, called PACA (Power-controlled Access with Collision Avoidance), improves both energy consumption and throughput, by reducing the energy used for most packet transmissions and by allowing simultaneous transmissions by different nodes, depending on the location of the respective receivers. PACA also improves the fairness among contending flows, in terms of the channel access time-share. I perform an extensive set of ns -2 simulations to study the impact of factors such as offered load, topology, number of flows, and node mobility on the performance of the proposed protocol and compare it to the IEEE 802.11 MAC protocol. The performance improvements are more pronounced in clustered networks with localized source-destination pairs because they utilize the available spectral reuse more efficiently.