The nine articles in this special section focus on the future of fifth generation (5G) millimeter wave systems. 5G communications will face a complete set of significant challenges, such as ultra-high system capacity due to the traffi c demand, massive device connectivity, ultra-low latency, reduction in energy consumption, and high quality of experience. In that context, 5G is called to produce a complete revolution in the way users can access content and services in their general activity across daily life. The evolution of communication systems has a direct and key role, offering major capacity and communication possibilities through the smart use of the available bandwidth and the propagation channel, and the deployment of higher frequencies at millimeter-wave (mmWave) frequency bands. The articles in this section present recent advances, technical aspects, and challenges surrounding mmWave 5G systems at the physical level so that the professionals involved in 5G definition and development can be aware of the technical challenges that arise in such systems.