The papers consist of correspondence, memoirs, and printed materials. The correspondence is made up of letters sent by his mother, Olǵa Kostyleva, from Petrograd in 1916-1919. Kostylev's extensive manuscript memoirs (522 p.) discuss his life from his childhood and university education in St. Petersburg up into World War I. Also included are issues and clippings from "Slovo" and "Rus"́ with articles by Kostylev, and clippings from "Poslednie Novosti" by various newspapers.