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.

The collection consists primarily of correspondence and manuscripts. There are letters from Korneĭ Chukovskiĭ, Mikhail Karpovich, Andre Mazon, Vladimir Nabokov, and Evgeniĭ Zami︠a︡tin. There is also one item each from Sergeĭ Esenin, Pavel Mili︠u︡kov, Ivan Pavlov, and Nikolaĭ Roerich. Manuscripts include photocopies of poems by Korneĭ Chukovskiĭ, Sergeĭ Esenin, and Boris Pasternak. There are subject files on Dostoevskiĭ, Turgenev, Soviet education, and Slavic studies in the United Studies, and a photograph of Isaak Babel ́with his daughter.

Besides correspondence, there are a few manuscripts, and also biographical information on many of the authors. Among the correspondents are Ivan Bunin, Vladimir Nabokov, Alekseĭ Remizov, Gleb Struve, and Boris Vysheslavt︠s︡ev.

The collection consists of correspondence, manuscripts, documents, a photograph, and printed material, primarily from the period 1941-1957. Included are letters from Ivan Bunin, Marc Chagall, Mikhail Karpovich, Vasiliĭ Maklakov, W. Somerset Maugham, Vladimir Nabokov, Ili︠́a︡ Repin, Edmund Wilson, Boris Zaĭt︠s︡ev and many others. Manuscripts of his works include "Istoki""Nachalo kont︠s︡a""Zhivi, kak khochesh"́, and "The Escape" (English translation of "Begstvo"), such shorter tales as "Noch ́v terminale""Povest ́o smerti", and "Ulḿskai︠a︡ noch"́, as well as numerous articles, book reviews and essays. There are financial records for "Novyĭ Zhurnal", which Aldanov helped found, and the clippings are mainly articles about Aldanov. There is one late photograph of Aldanov.