Abstract : An ad hoc network is a collection of nodes that communicate over wireless links in a multi-hop fashion without any fixed infrastructure. One of the main challenge in such networks is Medium Access Control. The IEEE 802.11 standard provides a communication mode that is suitable for ad hoc networks. However, the MAC (Medium Access Control) protocol described in 802.11 shows some fairness and efficiency issues. In this thesis I evaluate the performances of existing wireless protocols and highlighted the performance issues thanks to stochactic process algebra. Based on these results I designed two MAC protocols (MadMac and PAS) for wireless ad hoc networks and wireless LANs. Our protocols are different from those presented in the literature because they initially address the trade-off between efficiency and fairness. Thus, our proposed solutions are both efficient and fair.