This paper provides a characterization of fully implementable outcomes using undominated Nash equilibrium, i.e. a Nash equilibrium in which no one uses a weakly dominated strategy. The analysis is conducted in general domains in which agents have complete information. Our main result is that with at least three agents any social choice function or correspondence obeying the usual no veto power condition is implementable unless some players are completely indifferent over all possible outcomes. This result is contrasted with the more restrictive implementation findings with either (unrefined) Nash equilibrium or subgame perfect equilibrium.

We wish to thank the National Science Foundation for financial support. Profess or Palfrey also thanks the Exxon Educational Foundation and the Alfred P. Sloan Foundation for supporting his fellowship at the Center for Advanced Study in the Behavioral Sciences. We have benefited from comments by seminar participants at Carnegie-Mellon, Penn, Princeton, Stanford, SUNY-Buffalo, and USC, and from discussions with John Moore.

Submitted - sswp649.pdf