Every day, ad hoc networks demonstrate their importance in daily life via the benefits they bring to services in different areas of economic, social and cultural activity. This chapter introduces ad hoc networks and their different characteristics. It discusses the medium access phenomenon and the major problems present in the Medium access control (MAC) layer. The energy factor is of primary importance in the management and control of ad hoc networks, notably in the evaluation of routing and medium access protocols. Finally, the chapter explains the impact of energy on the functioning of ad hoc networks and the relationship between the effectiveness of these protocols and energy consumption.