The fast expansion of new wireless devices and applications over the last ten years has resulted in a massive increase in the demand for wireless radio spectrums. The existing fixed spectrum assignment strategy hinders efficient spectrum use. Much of the licensed spectrum has been underutilized due to this approach. To solve the spectrum efficiency problem, the idea of Cognitive Radio Networks (CRNs) has gained traction in recent years. Thanks to CRNs, Wi-Fi users can adjust their operational parameters best to suit their interactions with the surrounding radio environment. This paradigm aims to improve spectrum utilization through the dynamic allocation and sharing of spectrum resources. One of the most critical issues affecting the design and performance of traditional networks, such as Wireless Sensor Networks (WSNs), is localization. Location information is crucial for network design as primary users (PUs), key components of CRNs, have priority in using licensed spectrum. The challenge lies in accurately determining the location of sensor nodes within the network and determining the exact location where an event occurs. Precise information about the location of PUs is of great importance in CRNs. In this chapter, the issue of localization in CRNs is discussed in detail from an algorithmic point of view.