After the First Opium War (1839–1842), British and American merchants negotiated with Chinese officials in Shanghai to work out the framework of the new treaty port regime. One key player in these negotiations was Wu Jianzhang, a Cantonese merchant who became circuit intendant of the Shanghai region. Wu, however, also had links to Cantonese sailors and anti-Qing secret societies. When the Small Swords Society took Shanghai in 1853, he found himself entangled in conflicting responsibilities and networks. Foreign traders and Chinese officials regarded Wu, like other middlemen on the Chinese coast, with a mixture of respect and distrust. Wu's situation, however, was not unique to the mid-nineteenth century. This article compares Wu to other intermediaries who played similar roles in the sixteenth and late nineteenth centuries, in order to show the ways in which Wu, his predecessors, and those who followed in his footsteps connected China to the wider world by navigating the treacherous waters of diplomacy, war, and commerce. The work of John K. Fairbank, who in the 1950s pioneered the study of such people as Wu Jianzhang, can find new meaning in the twenty-first century, enabling us to understand the transnational implications of China's local social history.