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, manuscripts, notes, documents, photographs and printed materials of Frank. The collection reflects almost every aspect of his career, but especially his life in Germany, France, and England after his expulsion from Russia in 1922. Among the correspondents are Nikolaĭ Berdi︠a︡ev, Sergeĭ Bulgakov, Albert Einstein, Georgiĭ Florovskiĭ, Nikolaĭ Losskiĭ, Fedor Stepun, and Petr Struve; there are one or two items each from Vi︠a︡cheslav Ivanov, Bernard Pares, and Alekseĭ Remizov. There are also many letters from Semen Frank and his wife Tati︠a︡na to their son Viktor, and from Peter Struve's family to the Franks. Manuscripts for several of Frank's books are in the collection, such as "Svet vo tḿe" "Realńost ́i chelovek" and "Biografii︠a︡ P.B. Struve." Other manuscript materials by Frank include essays and lectures, outlines of courses he taught as a professor in Russia before his expulsion, and notebooks. There are also two poems by Vi︠a︡cheslav Ivanov. Among the printed works are Frank's Bible and offprints of his articles. There are photographs of Sergeĭ Bulgakov, Fedor Stepun, and of the Frank and Struve families.