With the deployment of 5G networks and the start of standardizing 5G-Advanced, both academia and industry are exploring actively into future technologies for next generation wireless communication systems. Reconfigurable intelligent surfaces (RISs) have been envisioned to reduce the energy consumption and improve the spectral efficiency of wireless networks by artificially re-configuring the propagation environment of electromagnetic waves. RIS-based transmission, in which the large number of small, low-cost, and passive elements on RIS only reflect the incident signal with an adjustable reflection amplitude and phase shift without requiring a dedicated energy source for radio frequency processing, decoding or encoding, is completely different from existing active relays and open up a new area of research for wireless communications. RISs are being discussed actively in regional and global standardization development organizations and are likely to become a critical component of 5G-Advanced networks.