This series contains Eilenberg's math notes and writings—a great many of which he left undated—and his math-related correspondence, a good deal of which is dated, at least in part. The series primarily includes: Eilenberg's hand-written math notes; what seem to be drafts or revisions of chapters of math books he authored or co-authored; photo-copies of math notes, chapter drafts, or revisions, often hand-annotated; correspondence with fellow-mathematicians about math questions or their joint efforts; possible lecture or class notes; copies of math papers or articles that Eilenberg filed in with his own notes (and which have been left in with his writings to preserve original order, as well as for the light they potentially shed on the genesis of his math work). Although most of the material in this series is in English, Eilenberg's student notebook is in Polish (Box 4, Folder 7), and other material is in French and German. Apart from Eilenberg's dated Polish notebook (1930-34), which fittingly begins the series, the rest of these mostly undated math notes and book chapters is organized by topic: the more substantial book chapters, revisions, and outlines are followed by a number of folders on various math topics, lecture or class notes, articles by Eilenberg, and math correspondence, respectively.