5G is a paradigm-shifting communications technology that is envisioned to provide an even wider range of high-quality services than 4G. It promises to offer high bandwidth and ultra-low latency, which are desirable not only for voice and mobile broadband, but also for new vertical industries such as healthcare, public transport, manufacturing, media and entertainment. Therefore, secure network architectures, mechanisms, and protocols are necessary to for a foundation of 5G to address potential security threats. This special issue is focusing on original research results and achievements by scientists, designers, and developers working on various issues and challenges related to 5G networks security.