Opponent Modeling in a Multi-agent System David Carmel and Shaul Markovitch Computer Science Department Technion, Haifa 32000 Israel Email: {carmel|shaulm}@cs.technion.ac.il Abstract Agents that operate in a multi-agent system need an efficient strategy to handle their encounters with other agents involved in that system. Searching for an optimal interactive strategy is a hard problem because it depends mostly on the behavior of the others. In this work, interaction among agents is represented as a repeated two-player game, where an agents' objective is to look for a strategy that maximizes their expected sum of rewards in the game. We assume that agents' strategies can be modeled as finite automata. A {\em model based reasoning} approach is presented as a possible method for learning an efficient interactive strategy. First, we describe how an agent should find an optimal strategy against a given model. Second, we present a heuristic algorithm that infers a model of the opponent's automata from its input/output behavior. A set of experiments that show the potential merit of the algorithm is reported as well.