This book constitutes the refereed proceedings of the 12th International Workshop on Security and Trust Management, STM 2016, held in Heraklion, Crete, Greece, in September 2016, in conjunction with the 21st European Symposium Research in Computer Security, ESORICS 2016. The 13 full papers together with 2 short papers were carefully reviewed and selected from 34 submissions. the focus on the workshop was on following topics: access control, data protection, mobile security, privacy, security and trust policies, trust models. .