The article provides a comprehensive overview of reconfigurable intelligent surfaces (RISs) in wireless communications, highlighting their potential to revolutionize future 6G and beyond networks. RISs are man-made electromagnetic (EM) surfaces that can be electronically controlled to manipulate the scattering, reflection, and refraction of radio waves, thereby enhancing signal quality and reducing the negative effects of natural propagation. The authors discuss the fundamental differences between RISs and other technologies like spatial modulation, relaying, and backscatter communications, emphasizing the unique features of RISs such as their passive nature, controllability, and full-band response. They also explore the theoretical performance limits of RIS-assisted systems and potential use cases in 6G networks. The article includes a detailed analysis of the two-ray channel model with and without RISs, demonstrating how RISs can significantly improve signal strength and reduce path loss. Additionally, it discusses the implementation of RISs using various technologies, such as meta-surfaces, liquid crystals, and varactor-tuned resonators. The authors further explore the use of RISs as low-complexity and energy-efficient transmitters, showing how they can enable virtual MIMO systems with a single RF chain. Overall, the article underscores the importance of RISs in addressing the challenges of future wireless networks and their potential to transform communication paradigms.The article provides a comprehensive overview of reconfigurable intelligent surfaces (RISs) in wireless communications, highlighting their potential to revolutionize future 6G and beyond networks. RISs are man-made electromagnetic (EM) surfaces that can be electronically controlled to manipulate the scattering, reflection, and refraction of radio waves, thereby enhancing signal quality and reducing the negative effects of natural propagation. The authors discuss the fundamental differences between RISs and other technologies like spatial modulation, relaying, and backscatter communications, emphasizing the unique features of RISs such as their passive nature, controllability, and full-band response. They also explore the theoretical performance limits of RIS-assisted systems and potential use cases in 6G networks. The article includes a detailed analysis of the two-ray channel model with and without RISs, demonstrating how RISs can significantly improve signal strength and reduce path loss. Additionally, it discusses the implementation of RISs using various technologies, such as meta-surfaces, liquid crystals, and varactor-tuned resonators. The authors further explore the use of RISs as low-complexity and energy-efficient transmitters, showing how they can enable virtual MIMO systems with a single RF chain. Overall, the article underscores the importance of RISs in addressing the challenges of future wireless networks and their potential to transform communication paradigms.