This book constitutes the refereed proceedings of the 19th International Conference on Group Decision and Negotiation, GDN 2019, held in Loughborough, UK, in June 2019. 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 17 full papers presented in this volume were carefully reviewed and selected from 98 submissions. They were organized in topical sections named: preference modeling for group decision and negotiations; collaborative decision making processes; conflict resolution; behavioral OR, and negotiation support systems and studies.