IEEE published the 802.11ac standard in 2013. This book summarizes and explains the specification of this new Wi-Fi standard by IEEE. This specification is extremely complex to understand and the learning curve is steep. This book tries to alleviate difficulties and be useful for people who will study or may even develop software for 802.11ac devices. It is not about a specific chipset or device. The content discusses in details the MAC and PHY layers. There is a special attention to channel aggregation, MIMO, MU-MIMO, beam-forming as well as how Linux integrates 802.11ac drivers in the kernel. Nevertheless it tries to be easy to read when possible and it gives much contextual information. Jean-Pierre had first hand access to 802.11ac information as one of Orange's delegates to IEEE.