Does “soft power” matter in international relations? Specifically, when the United States seeks cooperation from countries around the world, do the views of their publics about US foreign policy affect the actual foreign policy behavior of these countries? The authors examine this question using multinational surveys covering fifty-eight countries, combined with information about their foreign policy decisions in 2003, a critical year for the US. They draw their basic conceptual framework from Joseph Nye, who uses various indicators of opinion about the US to assess US soft power. But the authors argue that his theory lacks the specificity needed for falsifiable testing. They refine it by focusing on foreign public opinion about US foreign policy, an underemphasized element of Nye's approach. Their regression analysis shows that foreign public opinion has a significant and large effect on troop commitments to the war in Iraq, even after controlling for various hard power factors. It also has significant, albeit small, effects on policies toward the International Criminal Court and on voting decisions in the UN General Assembly. These results support the authors' refined theoretical argument about soft power: public opinion about US foreign policy in foreign countries does affect their policies toward the US, but this effect is conditional on the salience of an issue for mass publics.