  How important are leaders' actions in facilitating coordination? In this
paper, we investigate their signaling role in a global games framework. A
perfectly informed leader and a team of followers face a coordination problem.
Despite the endogenous information generated by the leader's action, we provide
a necessary and sufficient condition that makes the monotone equilibrium
strategy profile uniquely $\Delta$-rationalizable and hence guarantees
equilibrium uniqueness. Moreover, the unique equilibrium is fully efficient.
This result remains valid when the leader observes a noisy signal about the
true state except full efficiency may not be obtained. We discuss the
implications of our results for a broad class of phenomena such as adoption of
green technology, currency attacks and revolutions.
