The archival holdings of the Rockefeller Archive Center (RAC) are a valuable resource for the history of expertise. I have used several of the RAC collections to write a social history of the interchange of knowledge between Polish social scientists and American internationalists in the 1920s and the 1930s. I would like to see this story as the Continental prehistory of American area studies. This report offers an overview of my work at the RAC, in particular, the types of materials I have looked through. It briefly discusses how the evidence enriched my understanding of the ways that expert knowledge traveled between Eastern Europe and the United States.