Ties between the United States (US) and the European Union (EU) rival those between any other pair of international actors. After all, no other regions of the world are as closely connected in economics, security and politics as Europe and the US. This comprehensive volume makes conceptual progress and empirical contributions in accounting for how EU-US relations have been impacted by a context of multiple EU crises alongside a parallel change in US policies. The authors find strong evidence to suggest that the transatlantic relationship is weakening. This is partly a consequence of the EU's internal policies, as it becomes more unified and autonomous of the US in some areas, while fragmenting in others. Most importantly, it is a consequence of the two actors' increasingly diverging perspectives and positions on international issues, institutions, norms and indeed the value of the transatlantic relationship. Although the long-term effects remain to be seen, it is likely that the cracks in the foundation of transatlantic relations will continue into the present and foreseeable future. This book was originally published as a special issue of the Journal of European Integration.