This essay examines how internationalization has been a part of the history of the History of Science Society (HSS) from its establishment in 1924 to the present. Although the HSS remains a US-based society and its annual meetings are held primarily in the US, attended by mostly US-based scholars, we argue that there has always been a strong commitment to internationalism that continues to this day. We walk through the hundred years of the Society in four phases, namely the Sarton (...) years (1924–52), the coming-of-age of the field in America (1953–88), the opening up of the HSS to the world (1989–99), and the new millennium (2000–present). We end with a concluding section to elucidate how the Society has transitioned beyond Sarton as it goes into its second centenary. Our sources of evidence include interviews with select past HSS presidents, founders and chairs of HSS interest groups and forums, statistics of HSS membership to be found in the Smithsonian archives and HSS Newsletters, and distribution and patterns of Society-awarded prizes. We also take note of the growing numbers of roundtables and panels on global and non-Western history of science at HSS annual meetings since the 2010s. As we celebrate the HSS Centennial, it is important to reflect on the one hundred years of the Society’s engagement with internationalizing the history of science. (shrink)