The international conference "Group Decision and Negotiation (GDN) 2006" aims at bringing together researchers in the areas of Group Decisions, Negotiations, and Negotiation Support Systems. Participants share a common research focus on complex decision problems, which involve multiple stakeholders as well as the different information sets. The interdisciplinary research does not only seek to improve our understanding of group decision, negotiations, and market processes, but also to support decision makers, negotiators, and market engineers in achieving better outcomes.