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.

Papers of E.I. Zami︠a︡tin. The papers consist of correspondence, manuscripts, notes, and clippings. There are 9 letters by Konstantin Fedin, 3 by Boris Grigorév, and 1 or 2 each by Henri Barbusse, Cecil B. DeMille, Andrʹe Maurois, Alekseĭ Remizov, and Zami︠a︡tin himself. The manuscripts are chiefly brief or fragmentary works, including film scenarios, summaries of plays, essays, lectures, notes, and fragments. Longer works include the "Afrikanskiĭ gost́" lectures on prose given in 1920, and the posthumously published novel "Bich bozhiĭ" and "Lit︠s︡a". Also included are clippings on Zami︠a︡tin, chiefly from Soviet, Czech, French and Russian emigre periodicals, also transcripts of selected correspondence and manuscripts in the collection.