L. Busoniu, R. Babuska, and B. De Schutter, "Multi-agent reinforcement learning: An overview," Chapter 7 in Innovations in Multi-Agent Systems and Applications - 1 (D. Srinivasan and L.C. Jain, eds.), vol. 310 of Studies in Computational Intelligence, Berlin, Germany: Springer, pp. 183-221, 2010.
Multi-agent systems can be used to address problems in a variety of domains, including robotics, distributed control, telecommunications, and economics. The complexity of many tasks arising in these domains makes them difficult to solve with preprogrammed agent behaviors. The agents must instead discover a solution on their own, using learning. A significant part of the research on multi-agent learning concerns reinforcement learning techniques. This chapter reviews a representative selection of Multi-Agent Reinforcement Learning (MARL) algorithms for fully cooperative, fully competitive, and more general (neither cooperative nor competitive) tasks. The benefits and challenges of MARL are described. A central challenge in the field is the formal statement of a multi-agent learning goal; this chapter reviews the learning goals proposed in the literature. The problem domains where MARL techniques have been applied are briefly discussed. Several MARL algorithms are applied to an illustrative example involving the coordinated transportation of an object by two cooperative robots. In an outlook for the MARL field, a set of important open issues are identified, and promising research directions to address these issues are outlined.