In this article, we argue that the public will tolerate significant numbers of U.S. combat casualties under certain circumstances. To be sure, the public is not indifferent to the human costs of American foreign policy, but casualties have not by themselves driven public attitudes toward the Iraq war, and mounting casualties have not always produced a reduction in public support. The Iraq case suggests that under the right conditions, the public will continue to support military operations even when they come with a relatively high human cost. Our core argument is that the U.S. public’s tolerance for the human costs of war is primarily shaped by the intersection of two crucial attitudes: beliefs about the rightness or wrongness of the war, and beliefs about a war’s likely success. The impact of each attitude depends upon the other. Ultimately, however, we and that beliefs about the likelihood of success matter most in determining the public’s willingness to tolerate U.S. military deaths in combat.