This essay seeks to reconstruct Claudio Guillen's life at Harvard University, where he was educated as a comparatist along with some of the best scholars at that time, and where he taught his last years in the United States. This review of the professional and personal trajectories of Claudio Guillen helps us to understand the evolution of the discipline of Comparative Literature at Harvard University within the framework of postwar American comparatism, the literary studies of Claudio Guillen himself and his effort to promote the discipline of Comparative Literature in Spain, as well as the particular social circumstances of Spanish intellectuals and their families in exile. For all these matters, the administrative and personal documentation kept in the Harvard Archives is essential.