This book constitutes the proceedings of the 17th International Workshop on Security and Trust Management, STM 2021, co-located with the 26th European Symposium on Research in Computer Security, ESORICS 2021. The conference was planned to take place in Darmstadt, Germany. It was held online on October 8, 2021, due to the COVID-19 pandemic. The 10 papers presented in this volume were carefully reviewed and selected from 26 submissions. They were organized in topical sections on applied cryptography; privacy; formal methods for security and trust; and systems security.