This chapter discusses the evolution of wireless local area networks (WLAN). It explains the development of Institute of Electrical and Electronic Engineers (IEEE) 802.11 standards. The chapter proivdes the potential benefits of using WLANs. It analyses the performance issues of WLANs Discuss commonly used performance investigation methodology for WLANs. WLANs are currently being used as an attractive alternative, or complement, to wired local area networks in many educational and commercial organizations worldwide. For instance, New Zealand universities have reduced their need to outfit additional computer laboratories by setting up WLANs in the library and other study areas where students can connect their notebooks for accessing Intranet as well as the Internet. The IEEE released the 802.11 standard for WLAN in 1997. The specification requires a data transfer rate of 1 and 2 Mbps while retaining compatibility with existing LAN hardware and software infrastructure. The chapter also presents an overview of the key concepts discussed in this book.