Papers include Kagan's correspondence, photographs, printed materials and audio tapes. All letters in the collection date from 1938-39, when he had moved his Petropolis operations to Brussels; there are items by Vladislav Khodasevich, Vladimir Nabokov, and Mikhail Osorgin, and others. Among the photographs are pictures of Ivan Bunin, Konstantin Fedin, and Evgeniĭ Zami︠a︡tin. Printed materials consist chiefly of books published by his firms; some of the books are inscribed, for example by Nikolaĭ Berdi︠a︡ev and Lev Karsavin. Included is a lengthy taped interview of Kagan by Marc Raeff in which Kagan discuses his life and publishing activities.

Correspondence and manuscripts of Zaĭt︠s︡ev. This collection covers from the 1920's into the 1960's. There is correspondence from many other emigre writers. The largest groups of cataloged letters are by Mark Aldanov (105 items), Ivan Bunin (161), Archimandrite Kiprian (104), Alekseĭ Remizov (48), and Nadezhda Teffi (101). There are also items by Boris Bugaev (Andreĭ Belyĭ), Vi︠a︡cheslav Ivanov, Vladislav Khodasevich, Sergeĭ Lifaŕ and Boris Pasternak. Zaĭt︠s︡ev's manuscripts in the collection include some of his major works, such as "Puteshestvie Gleba" "Dom v Passi" "Zhizn ́Turgeneva" and "Zhukovskiĭ". In addition, the collection has a book and a pamphlet, both inscribed by Zaĭt︠s︡ev.