When applied to groups, the revelation principle postulates a Bayesian-Nash behavior between agents. Their binding agreements are unenforceable or the principal can prevent them at no cost. The authors analyze instead a mechanism design problem in which the agents can communicate between...

In a public good environment with positively correlated types, we characterize optimal mechanisms when agents have private information and can enter collusive agreements. First, we prove a weak-collusion-proof principle according to which there is no restriction for the principal in offering...

When a decision rule is implemented using a Bayesian incentive compatible mechanism in which the messages are publically obser vable, the players' information is augmented by their observation of each others' strategies. In this paper the authors study the set of Bayesian implementable decision...

This paper studies a two-period principal/agent relationship run by short-term contracts. The principal updates the incentive scheme aft er observing the agent's first-period performance. The agent has superio r information about his ability. The principal offers a first-period incentive scheme...