This paper presents the Darwin Correspondence Project’s work with Cambridge University Digital Library on Epsilon (Epistles of Science in the Long Nineteenth century). Following the work of Early Modern Letters Online and correspSearch, Epsilon uses Correspondence Metadata Interchange Format in TEI and open-source indexing tools to combine the work of large editorial projects, individual scholars, archive catalogues, and print correspondence sources to sift through the large volume of nineteenth century letters. The paper outlines our intentions to open a space that allows researchers to have a better sense of the rich variety scientific activities and actors during the period in which science as a professional discipline was being formed.