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 issues arising in the design of on-line environments whose participants are human and software.Teams: The papers consider different aspects of team working: what kinds of knowledge sharing best contribute to effective team performance and how to organize ateam to function effectively in different kinds of scenarios.Rights and Values: The papers examine complementary issues that influence the effective design of normative systems, namely how to detect opportunism so that it may be discouraged, how individuals values influence (collective) decision-making processes and how rights and powers relate to value and conflict resolution in nested organizational structures.