This volume presents the latest developmentsinthegrowingareaofresearch at the interface of argumentation theory and multiagent systems. This area has grown tremendously with many papers appearing in the recent special issue of the Arti?cial Intelligence Journal on "Argumentation" and the special issue of IEEE Intelligent Systems on "Argumentation Technologies. " Over the last few years, argumentation has been gaining increasing imp- tance in multiagent systems, mainly as a vehicle for facilitating rational int- action (i. e. , interaction which involves the giving and receiving of reasons). This is because argumentation provides tools for designing, implementing, and a- lyzing sophisticated forms of interaction among rational agents. Argumentation hasmadesolidcontributionstothe practiceofmultiagentdialogues. Application domains include: legal disputes, business negotiation, labor disputes, team f- mation, scienti?c inquiry, deliberative democracy, ontology reconciliation, risk analysis, scheduling, and logistics. A single agent may also use argumentation techniquestoperformitsindividualreasoningbecauseitneedstomakedecisions under complex preferences policies, in a highly dynamic environment. Most papers in this volume appeared in the proceedings of the 4th Int- national Workshop on Argumentation in Multiagent Systems (ArgMAS 2007), which took place in Honolulu, USA, in conjunction with the International Joint Conference on Autonomous Agents and Multiagent Systems (AAMAS). This continues the success of the ArgMAS workshop series, which took place in t- dem with AAMAS in New York in 2004,Utrecht in 2005,and Hakodatein 2006.