This book constitutes the refereed proceedings of the 21st International Conference on Group Decision and Negotiation, GDN 2021, which was planned to be held in Toronto, ON, Canada, during June 6-10, 2021. The conference was held virtually due to the COVID-19 pandemic.

The field of Group Decision and Negotiation focuses on decision processes with at least two participants and a common goal but conflicting individual goals. Research areas of Group Decision and Negotiation include electronic negotiations, experiments, the role of emotions in group decision and negotiations, preference elicitation and decision support for group decisions and negotiations, and conflict resolution principles.

The 12 full papers presented in this volume were carefully reviewed and selected from 74 submissions. They were organized in topical sections as follows: pandemic responses; preference modeling for group decision and negotiation; conflict resolution; and collaborative decision making processes.