This book constitutes the refereed proceedings of the 26th International Conference on Group Decision and Negotiation, GDN 2026, held in Katowice, Poland, during June 28–July 1, 2026.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 15 full papers included in these proceedings were carefully reviewed and selected from 89 submissions. They were organized in topical sections as follows: AI and Negotiation Analytics; Preference Modeling in Group Decision Contexts; and Conflict Resolution in Complex Decision Contexts.
