Jacob investigates what it meant to be cosmopolitan in Europe during the early modern period. Then--as now--being cosmopolitan meant the ability to experience people of different nations, creeds, and colors with pleasure, curiosity, and interest. Yet such a definition did not come about automatically, nor could it always be practiced easily by those who embraced its principles. Cosmopolites had to strike a delicate balance between the transgressive and the subversive, the radical and the dangerous, the open-minded and the libertine. Jacob traces the history of this precarious balancing act to illustrate how ideals about cosmopolitanism were eventually transformed into lived experiences and practices. From the representatives of the Inquisition who found the mixing of Catholics and Protestants and other types of "border crossing" disruptive to their authority to the struggles within urbane masonic lodges to open membership to Jews, Jacob also charts the moments when the cosmopolitan impulse faltered.