This book constitutes the proceedings of the Third International Workshop on Emerging Technologies for Authorization and Authentication, ETAA 2020, held in Guildford, UK, in September 2020. The 10 full papers presented in this volume were carefully reviewed and selected from 15 submissions. The conference was planned at University of Surrey, Guildford, UK. Due to COVID-19 outbreak, ESORICS conference and affiliated workshop will be held online. The workshop presents new techniques for biometric and behavioral based authentication,  and authorization in the IoT and in distributed systems in general, and much more.