Since the base version of IEEE 802.11 released in 1997, wireless local area network (WLAN) has been developing rapidly, and it has gone through many versions and amendments. The 802.11 protocol is now very sophisticated through 20 years of modification. Therefore, it is very hard to understand all improvements, which confuses researchers sometimes, making it not easy to discover the trend of development. This paper tries to summarize the key technologies that pushed WLAN forward among all important amendments, and then lists the latest research focus for the next generation of 802.11 family. The paper would provide assist researchers to find their field of interest.