Mediation has competing short- and long-term effects. In the short run, the actors are better able to identify and settle on a mutually satisfying outcome. In the long run, mediation can create artificial incentives that, as the mediator's influence wanes and the combatants' demands change, leave the actors with an agreement less durable than one that would have been achieved without mediation. This article tests the observable implications from this logic using a set of international crises from 1918 to 2001. The results reconcile findings in the previous literature that inconsistently portray the effectiveness of mediation.