What makes international threats credible? Recent theories point to domestic audience costs-the domestic price a leader would pay for making foreign threats and then backing down+ This article provides the first direct evidence of audience costs+ The analysis, based on experiments embedded in public opinion surveys, shows that audience costs exist across a wide range of conditions and increase with the level of escalation+ The costs are evident throughout the population, and especially among politically active citizens who have the greatest potential to shape government policy+ Finally, preliminary evidence suggests that audience costs arise because citizens care about the international reputation of the country or leader+ These findings help identify how, and under what conditions, domestic audiences make commitments credible+ At the same time, they demonstrate the promise of using experiments to answer previously intractable questions in the field of international relations+ What makes international commitments credible? The answer may lie, in part, at the intersection of foreign affairs and domestic politics+ Recent models of international relations assume that leaders would suffer "domestic audience costs" if they issued threats or promises and failed to follow through+ Citizens, it is claimed, would think less of leaders who backed down than of leaders who never committed in the first place+ In a world with audience costs, the prospect of losing domestic support-or even office-could discourage leaders from making empty threats and promises+ The concept of domestic audience costs is now central to theories about military crises, and researchers have incorporated similar ideas into Despite the prominence of audience costs in international relations theories, it remains unclear whether and when audience costs exist in practice+ Most empirical work on the topic is indirect+ Fearon conjectured that audience costs are higher in democracies than in autocracies and explained why this gap would cause the two types of regimes to behave differently+ 2 Researchers have, therefore, checked for correlations between democracy and foreign policy+ 3 Although valuable, these tests do not reveal whether the effects of democracy stem from audience costs or from other differences between political regimes+ One could try to study audience costs directly, perhaps by examining the historical fate of leaders who issued threats and then backed down+ The problem, which international relations scholars widely recognize, is strategic selection bias+ 4 If leaders take the prospect of audience costs into account when making foreign policy decisions, then in situations when citizens would react harshly against backing down, leaders would tend to avoid that path, leaving little opportunity to observe the public backlash+ It would seem, therefore, that a direct and unbiased measure of audience costs is beyond reach+ This article aims to solve the empirical conundrum+ The analysis is based on a series of experiments embedded in publi...