This book constitutes the thoroughly refereed post-conference proceedings of the 12th International Workshops on Coordination, Organizations, Institutions and Norms in Agent Systems, COIN 2016. The workshop COIN@AAMAS 2016 was held in Singapore, Singapore, in May 2016, and the workshop COIN@ECAI 2016 was held in The Hague, The Netherlands, in August 2016. The 9 full papers were carefully reviewed and selected from 15 submissions for inclusion in this volume. They cover the following topics: Social Issues: The papers focus on the security of personal data, support for self-care for individuals with chronic conditions, analysis of the risk of information leakage in social networks, and an analysis of