We prove the folk theorem for the Prisoner's dilemma using strategies that are robust to private monitoring. From this follows a limit folk theorem: when players are patient and monitoring is sufficiently accurate, (but private and possibly independent) any feasible individually rational payoff...

A population of players of players is randomly matched to play a normal form game G. The payoffs in this game represent the fitness associated with the various outcomes. Each individual has preferences over the outcomes in the game and chooses an optimal action with respect to those preferences....

In repeated games, simple strategies such as Grim Trigger, while strict equilibria when monitoring is perfect, can fail to be even approximate Nash equilibria when monitoring is private, yet arbitrarily close to perfect. That is, they fail to be robust to private monitoring. In this paper, it is...