A vast array of new Wi-Fi devices emerges every year, facilitating short-range wireless communication, entertainment, online education, home office work, and smart home applications. However, the congestion in the 2.4 GHz and 5 GHz bands is becoming increasingly evident due to the limited number of available Wi-Fi channels. When numerous Wi-Fi devices compete for these scarce channel resources, collisions occur, severely degrading network performance and compromising the user experience. The Wi-Fi 6 standard, officially ratified in 2019, specifically aims to enhance performance and improve service quality, with a primary focus on addressing the challenges posed by high-density environments. Through this chapter, readers will gain insights into the evolutionary advancements in the Wi-Fi 6 Physical Layer and Medium Access Control specification, uncovering how this technology effectively enables a higher number of concurrent connections and sustains optimal performance levels in densely populated scenarios. This exploration encompasses the pivotal Wi-Fi 6 innovations, detailed new changes in the Wi-Fi 6 specification, and the introduction of support for the 6 GHz spectrum, which is known as Wi-Fi 6E.