What motivates states to act the way they do? This book focuses on a particular kind of motivation inclining a state to challenge the existing norms, rules, and institutions of international order. Specifically, it addresses the concept of revisionism, which has loomed large in international relations narratives but has remained largely understudied until recently. The authors offer a critique of the existing discourse on revisionism and investigate the historical origin and evolution of the foreign policy orientations of revisionist states in the past. They moreover introduce an ensemble of indicators to discern and compare the extent of revisionist tendencies on the part of contemporary China and the United States. Questioning the facile assumption that past episodes will repeat in the future, they argue that “hard” revisionism relying on war and conquest is less viable and likely in today’s world. Instead, “soft” revisionism seeking to promote institutional change is more relevant and likely. They attend especially to contemporary Sino-American relations and conclude that much of the current discourse based on power-transition theory is problematic. Contrary to this theory, a dominant power is not inevitably committed to the defense of international order, nor does a rising power usually have a revisionist agenda to challenge this order. The transformation of international order does not necessarily require a power transition between China and the United States, nor does a possible power transition between these two countries necessarily augur war.