This paper traces discourse and practices among Jewish communal leaders in Western Europe and the United States regarding the need for Jewish missions to China and Ethiopia. Though thousands of miles apart, China and Ethiopia became closely entwined in their racial imagination. Beginning in the 1840s, the Jewish international press depicted both as biblical lost tribes, languishing in isolation and ignorance, and in need of a guiding hand with the mounting threat of Christian missionizing. Jewish communal leaders began to call for Jewish missions in the 1850s, and they looked to contemporary scientific, evangelical, and civilizing missions as models, merging elements from all three. Throughout the 1860s, in debates over who should lead a Jewish mission, three different types surfaced: an explorer, rabbinic emissary, and Orientalist. Each of these reframed prophetic calls for the return of the lost tribes within a modern scientific and imperial project. Drawing on the work of Sylvia Wynter, I argue that these communities in China and Ethiopia came to serve as boundary markers, demarcating the outer limits of the Jewish world, of Jewishness, and Judaism as it became increasingly circumscribed through theological, behavioral, and racial norms. Not only does this upend assumptions about Jewish solidarity and internationalism, but it also points to how missionizing was deployed by minoritized communities in the nineteenth century.