The current burst of work on regimes or, more broadly, on international institutions, reflects an emerging sense—especially among Americans—that the international order engineered by the United States and its allies in the aftermath of World War II is eroding rapidly and may even be on the verge of collapse. But is the resultant surge of scholarly work on international regimes any more likely to yield lasting contributions to knowledge than have other recent fashions in the field of international relations? The jury will remain out until a sustained effort is made to evaluate the significance of regimes or institutions more broadly, as determinants of collective behavior at the international level.