Worldwide Interoperability for Microwave Access (WiMAX) aims to provide high-speed, high-bandwidth, and high-capacity Broadband Wireless Access (BWA) for residential as well as enterprise applications. WiMAX is designed to provide high data rate multimedia services, e.g., voice, data, Internet, email, instant messenger, and games. The security of WiMAX has been under researchers’ scrutiny for the last few years. Both architectures and protocols on WiMAX security have been extensively studied in academics and industries. Several articles, survey reports, and research papers have been published and a number of flaws have been highlighted in the literature. The IEEE Committee has published several revisions of the IEEE 802.16 standard since its initial release in 2001, but many of the vulnerabilities have still been left unattended in the standard. Ensuring the security of these complex and yet resource constraint systems has emerged as one of the most pressing challenges. The aim of this Special Issue is to bring together researchers and practitioners in related areas and to encourage interchange and cooperation under the context of WiMAX security between the research community and the industrial/ consumer community. With regard to such cyber security aspects, there is an increasing demand for measures to guarantee and fully attain the authentication, confidentiality, data integrity, privacy, access control, non-repudiation, and availability of system services. The first paper in this Special Issue by Barghava et al.: discusses security problems, with a focus on collaborative attacks, in the WiMAX scenario. The WiMAX protocol suite, which includes but is not limited to DOCSIS, DES, and AES, consists of a large number of protocols. The authors presented briefly the WiMAX standard and its vulnerabilities. They pinpoint the problems with individual protocols in the WiMAX protocol suite, and discuss collaborative attacks on WiMAX systems. Then several typical WiMAX attack scenarios were presented, including: bringing a large number of attackers to increase their computation power and break WiMAX protocols; assembling a sufficient number of attackers to influence the decision-making of core machines, which includes routing attacks and Sybil attacks, and exploiting implementations that do not conform to the WiMAX specification completely, causing interoperability problems among various protocols, including the ones in typical WiMAX/WiFi/LAN deployment scenarios. Then the authors presented theoretical models and practical solutions to profile, model, and analyze collaborative attacks in WiMAX. Employed attack graphs to vulnerability were analyzed. Experimental results are carried out to verify the models and validate the analysis. Du et al.: study the rekeying issue in IEEE 802.16e WiMAX networks. The existing rekeying scheme— the Multicast and Broadcast Rekeying Algorithm (MBRA) unicasts new keys to each subscriber station (SS). This scheme does not scale well since it incurs large communication overheads when the number of SSs increases. In this work, first a general tree-based rekeying scheme was proposed, which is more efficient than the MBRA. Also formulate an optimization problem to determine the optimal tree structure for given number of SSs. Furthermore, a novel and efficient rekeying scheme for WiMAX networks was presented. The new rekeying scheme utilizes efficient