New Department Working Paper

I study a general model of repeated interactions between long-run players who have no probabilistic beliefs about the environment in which future interactions will take place. I introduce a notion of equilibrium, where at each history players minimize their regret from forgoing an alternative strategy under the worst-case sequence of future games, taking as given the strategies of other players. I derive a recursive characterization of equilibrium outcomes for fixed discounting, as well as a folk theorem. I demonstrate the tractability of the characterization in applications to risk-sharing and partnership games.