Conflict Resolution.- Nash Stability in a Multi-Objective Graph Model with Interval Preference Weights: Application to a US-China Trade Dispute.- A Novel Conflict Resolution Model Based on the Composition of Probabilistic Preferences.- Analysis of Disputed Territories in the Barents Sea.- A Novel Method for Eliminating Redundant Option Statements in the Graph Model for Conflict Resolution.- Alternatives vs. Time – Measuring the Force of Distinct Sources of Bargaining Power.-Preference Modeling for Group Decision and Negotiation.- Influence Across Agents and Issues in Combinatorial and Collective Decision-making.- A Characterization for Procedural Choice Based on Dichotomous Preferences over Criteria.- Influence Among Preferences and Its Transformation to Behaviors in Groups: An Agent-based Modeling and Simulation of Fertility Intention and Behavior.- Manipulability of Majoritarian Procedures in Two-Dimensional Downsian Model.- Intelligent Group Decision Making and Consensus Process.- PredictRV : A Prediction Based Strategy for Negotiations with Dynamically Changing Reservation Value.- Inferring Personality Types for Better Automated Negotiation.- Decision Rule Aggregation Approach to Support Group Decision Making.- Collaborative Decision Making Processes.- An Ontology for Collaborative Decision Making.- Decidio: A Pilot Implementation and User Study of a Novel Decision-Support System.

This book constitutes the refereed proceedings of the 20th International Conference on Group Decision and Negotiation, GDN 2020, which was planned to be held in Toronto, ON, Canada, during June 7–11, 2020. The conference was cancelled due to the Coronavirus pandemic. Nevertheless, it was decided to publish the proceedings, because the review process had already been completed at the time the cancellation was decided.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 14 full papers presented in this volume were carefully reviewed and selected from 75 submissions. They were organized in topical sections named: Conflict Resolution, Preference Modeling for Group Decision and Negotiation, Intelligent Group Decision Making and Consensus Process, Collaborative Decision Making Processes.