Device-to-device (D2D) communication stands out as a promising technology for future wireless networks. It enables direct communication between devices, improving latency, reliability, throughput, and power consumption. These reduce also network load and increases cellular coverage. In addition, a device can act as a relay between the base station and another device located outside. Therefore, D2D communication can help meet the requirements of future 5G (5th Generation) wireless networks (Pirinen in 1st International conference on 5G for ubiquitous connectivity, pp. 17–22, 2014). In this chapter, we will focus on energy consumption in direct and relayed D2D communications. We will study the basic model of D2D communication. This will be used for calculating the energy consumed by different proposed topologies. The study will be completed by evaluating the total energy consumed by each topology.