The relationship between a powerful US and some of the central multilateral organizations in global society is an essential feature of contemporary international relations. This text brings together a range of scholars to examine this crucial phenomenon. Its aims are two-fold: to describe and explain US behaviour in and towards a wide range of significant global and regional institutions; and secondly, to examine the impact of US behaviour on the capacity of each organization to meet its own objectives. The study explores US behaviour and its consequences for organizations based at the regional as well as the global levels, for those located in different regions of the world, and for such issue areas as security, economics, and the environment. Although focusing on the period since the 1990s, each chapter places its findings in a broader historical context.