Ambiguity can be used as a strategic device in some situations. To

demonstrate this, we propose and study a framework for normal form

games where players can use Knightian uncertainty strategically. In

such Ellsberg games, players may use Ellsberg urns in addition to

the standard objective mixed strategies. We assume that players are

ambiguity-averse in the sense of Gilboa and Schmeidler. While classical Nash equilibria remain equilibria in the new game, there arise

new Ellsberg equilibria that can be quite different from Nash equilibria. A negotiation game with three players illustrates this finding.

Another class of examples shows the use of ambiguity in mediation.

We also highlight some conceptually interesting properties of Ellsberg

equilibria in two person games with conflicting interests.