D2D communications can be prone to potential security threats. For example, D2D mobiles need to know who else is located nearby so as to pair up. If the location information is spoofed, the interference caused by wrongly paired D2D users can significantly lower the system performance. Additionally, D2D communications between neighboring D2D nodes provide alternative security approaches (physical-layer security) by using channel statistics. In this chapter, we will study the following two security problems in detail.