  In this paper I discuss truthful equilibria in common agency models.
Specifically, I provide general conditions under which truthful equilibria are
plausible, easy to calculate and efficient. These conditions generalize similar
results in the literature and allow the use of truthful equilibria in novel
economic applications. Moreover, I provide two such applications. The first
application is a market game in which multiple sellers sell a uniform good to a
single buyer. The second application is a lobbying model in which there are
externalities in contributions between lobbies. This last example indicates
that externalities between principals do not necessarily prevent efficient
equilibria. In this regard, this paper provides a set of conditions, under
which, truthful equilibria in common agency models with externalities are
efficient.
