This book constitutes the refereed proceedings of the 24th International Conference on Group Decision and Negotiation, GDN 2024, which took place in Porto, Portugal, during June 3-5, 2024. 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 13 full papers presented in this volume were carefully reviewed and selected from 100 submissions. They were organized in the following topical sections: Conflict Resolution; Preference Modeling for Group Decision and Negotiation; Collaborative and Responsible Negotiation Support Systems and Studies.