With the commercialization of the fifth generation (5G) wireless networks in 2019, developing the next generation wireless standard has been put on the agenda. To cope with the 1000x capacity requirements, the 5G wireless networks has adopted massive MIMO as a key enabling physical layer technology to boost the spectral efficiency. In addition, higher frequency band such as millimeter wave band is exploited to address the spectrum shortage problem. Looking ahead, it has been envisioned that

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... her scaling up the antenna number, such as ultra-massive MIMO and moving into even higher frequency band such as Terahertz (THz) band, are two promising directions. However, deploying thousands of antennas in the conventional approach is unsustainable due to the huge cost associated with the massive number of RF chains. Moreover, cost-effective and high-performance RF components working in the extremely high frequency band are currently not available. These challenges should be properly addressed before ultra-massive MIMO and THz technologies can be possibly implemented in practice. Recently, a novel concept, referred to as Reconfigurable Intelligent Surface (RIS), has emerged. The RIS is an artificial planar structure made of sub-wavelength unit cells, which can be coated on any environmental object, thereby providing a cost-effective way for the implementation of ultra-massive MIMO technology. In addition, RIS is extremely flexible and can work in a wide range of frequency band, ranging from microwave to visible light. More importantly, RIS can reflect an incoming electromagnetic wave and adjust its amplitude and phase in a controllable way. As such, RIS holds the potential to revolutionize the design of future wireless networks, and hence has gained considerable research interests. However, the application of RIS s in wireless communication is still in its infancy, and substantial research efforts are needed to gain a fundamental understanding. Motivated by this, this special issue is aimed at reporting the latest and most promising research advances on key architectures, modeling, analysis, design, and implementation of RIS-empowered wireless networks, and at envisioning new research directions in this emerging field of research. The topics of interest include, but are not limited to the following:  Physics-and electromagnetic-compliant modeling of RIS s  Channel modeling of RIS-empowered wireless networks  Information theoretical limits of RIS-empowered wireless networks  Transceiver design using RIS  High order modulation design for RIS transceivers  Channel estimation techniques for RIS-empowered wireless networks  Resource allocation in RIS-empowered wireless networks  Algorithms and protocols design/optimization for RIS-empowered wireless networks  Software-defined design and implementation of RIS-empowered wireless networks  AI-inspired control and orchestration of RIS-empowered wireless networks  Indoor/outdoor localization in RIS-empowered wireless networks  Distributed configuration and deployment of RIS-empowered wireless networks  Integration of RISs with state-of-the-art wireless technologies (e.g., small cells, Massive MIMO, millimeter-wave communications, visible light communications, THz communication, free space optics, Internet of Things, drones-aided communications, energy harvesting, etc.)  Experimental results and testbed implementations of RISs SCHEDULE