This book constitutes the proceedings of the 22nd Conference on Passive and Active Measurement, PAM 2021, which was planned to be held in Cottbus, Germany, in March 2021. Due to the Corona pandemic, the conference was organized as a virtual meeting. The 33 full papers presented in this volume were carefully reviewed and selected from 75 submissions. They were organized in topical sections named: COVID-19; web security; video streaming; TLS; staying connected; DoS; performance; network security; DNS; capacity; and exposing hidden behaviors. Due to the Corona pandemic, PAM 2021 was held as a virtual conference.