This book constitutes the proceedings of the Joint INFORMS-GDN and EWG-DSS International Conference on Group Decision and Negotiation (GDN), held in Toulouse, France, during June 1013, 2014.The GDN meetings aim to bring together researchers and practitioners from a wide spectrum of fields, including economics, management, computer science, engineering and decision science. The contributions report on research on individual and group decision support, negotiation and auction support and the design of systems and agents supporting such processes.From a total of 88 submissions, 31 papers were accepted for publication in this volume. The papers are organized into topical sections on collaborative decision making, auctions, knowledge decision support systems, multi-criteria decision making, multi-agent systems, negotiation analysis, preference analysis, data analysis, DSS / GDSS use, network analysisand semantic tools for group decision making.