This book constitutes the refereed proceedings of the 12th International Conference on Subject-Oriented Business Process Management, S-BPM ONE 2020, held in Bremen, Germany, in December 2020. Due to the COVID-19 pandemic the conference was held online.  The 10 full papers and 5 short papers were thoroughy reviewed and selected from 25 submissions. The volume also presents 1 keynote paper. The papers are thematically organized according to the following sections: subject-oriented business processing – syntax and semantics; cyber-physical and assistance systems; process mining and the Internet of actors and behaviors; Industry 4.0; various views on business process management.