The relationship between the United States and China, one country an established power, the other country a rising power, will decisively shape the 21st century. A more cooperative and stable strategic relationship between the two countries will make it easier to meet today’s global economic, political, security, social, and environmental challenges. Such a relationship will in turn allow both countries to focus scarce leadership attention, political capital, and economic resources on achieving their domestic priorities. By contrast, a more confrontational and troubled strategic relationship would undermine the security and well-being of both China and the United States. For these reasons, the importance but also the challenges of building toward a more stable and cooperative U.S.-China relationship are widely recognized in both countries today.