Harry H. Laughlin's main claim to fame was as director of the Eugenics Record Office at Cold Spring Harbor, Long Island, from which position he exerted considerable influence upon early twentieth-century campaigns to restrict immigration and to institute compulsory sterilization of the socially inadequate. Laughlin also had an absorbing fascination for the idea of a single world government. Over the course of forty years, he produced a voluminous body of mostly unpublished work on the subject. In examining Laughlin's musings on internationalism, this article provides a glimpse into how a leading American eugenicist would have projected onto the world stage the policies he was zealously endeavoring to implement at the domestic level. Laughlin sent samples of his work to many of America's leading internationalists. Their responses to Laughlin's ideas reveal much about the character of internationalism in the United States during the era of World War I, especially the extent to which his racist and imperialist assumptions were shared by other members of the internationalist movement. Consequently, this article provides yet another example of how liberal and conservative impulses were neither easily distinguishable nor mutually exclusive during the Progressive Era.