Richard von Glahn analyzes the movement of coin to illuminate the hey day enjoyed by East Asian maritime commerce during the period 1170–1270. The widespread substitution of paper money for bronze coin in China triggered a massive export of Chinese coin to Japan. These exports in turn stimulated the rapid monetization of Japan’s domestic economy, which further invigorated maritime commerce. A transnational network of merchants from Ningbo and Hakata emerged and achieved dominance over Sino-Japanese trade. In the port city of Hakata, Ningbo merchants developed personal and business ties with Japan’s kenmon elite—the warriors, courtiers, and religious institutions that dominated Japanese government and society—ties that proved crucial to their commercial success. As a result of these networks, China’s overseas commerce underwent a major reorientation, with Ningbo abruptly supplanting Quanzhou and Guangzhou as the main port of international trade.