The Fourth Workshop on Cooperative Games in Multiagent Systems (CoopMAS-2013) https://sites.google.com/site/coopmas2013/home May 6 or 7, 2013 Saint Paul, Minnesota, USA Co-located with the 12th International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2013) The use of cooperative game theory to study how agents should cooperate and collaborate, along with the related topic of coalition formation, has received growing attention from the multiagent systems, game theory, and electronic commerce communities. The workshop is intended to focus on topics in cooperation in multi-agent systems, cooperative game theory and cooperative solution concepts, formation of coalitions, negotiation between agents, joint decision making, and voting. Topics of interest include, but are not limited to: Cooperative game theory Coalition formation Joint decision making and voting Representation issues Negotiation Collaborative filtering Market and economics based...