Living with a Reluctant Hegemon addresses a striking puzzle in contemporary world politics: why have European states responded in varying ways to recent unilateralist tendencies in US foreign policy? The United States played a hegemonic leadership role in building the post-war multilateral order but has been reluctant to embrace many recent multilateral treaty initiatives championed by its traditional European allies, such as the Kyoto Protocol on climate change, the International Criminal Court, or the verification protocol to the Biological Weapons Convention. European responses to US objections, however, have varied across these different transatlantic controversies. In some cases, European decision-makers watered down or abandoned contested treaties, whereas in other disputes, they opted for regime-building excluding the US, that is, for a strategy of non-hegemonic cooperation.