This white paper provides an introduction to the technology used in the 802.11ax amendment to the 802.11 standard and an overview of receiver and transmitter test requirements. IEEE 802.11ax, also known as High Efficiency Wireless (HEW), provides mechanisms to more efficiently utilize the unlicensed spectrum bands (2.4 and 5 GHz) and improve user experience. It contains four main parts: core documents for the 11ax amendment development, 11ax goals and features, technology overview that covers key new parts of the IEEE 802.11ax draft, and test requirements for measuring key metrics such as EVM and adjacent channel rejection.