Thanks to the much larger geographical coverage and pleasing bandwidth of data transmissions, Wireless Metropolitan Area Networks (WMANs) have become widely accepted in many countries for everyday communications. Two of the main wireless technologies used in WMANs, the Worldwide Interoperability for Microwave Access (WiMAX, also known as Wireless Local Loop or WLL) and Long Term Evolution (LTE), have generated billions of dollars in the ever-growing wireless communication market. While the IEEE 802.16 standards for WiMAX and the 3GPP standards LTE are updated and improved almost annually, it is inevitable that current standards still contain a number of security vulnerabilities, potentially leading to various security attacks. To address the security concerns in these two WMANs technologies, this chapter presents the technical details of security aspects of WiMAX and LTE. More specifically, the key generation, authentication, data, and key confidentiality and integrity of both technologies are deliberated. The chapter ends with a discussion of the security vulnerabilities, threats, and countermeasures of WiMAX and LTE.