Correspondence, manuscripts, memoranda, receipts, certificates, financial and legal documents, envelopes, clippings, pamphlets, and other printed materials dealing with social and family relationships, the sons' education, professions, and military careers, the Mexican-American War and the Civil War, real estate and financial matters, and with the deaths and bequests of various family members. Among the cataloged correspondents are: Alexander Hamilton, John Church Hamilton, Gen. Schuyler Hamilton, Ralph Isaacs Ingersoll, Charles Augustus Peabody, Gen. J. Fred Pierson, Gen. Winfield Scott, Martin Van Buren, and a manuscript by George Washington.

Correspondence files of Roberts Brothers, pertaining to all departments, editorial, production, advertising, and sales. Also, some miscellaneous letters and documents, unrelated to Roberts Brothers, which deal with various legal matters, including those of Frederick D. Ely and of William A. Dunn, from 1838 until 1932, and letters to the Secretary of Harvard University from 1900 to 1907.

Correspondence, manuscripts, notes, memoranda, notebooks, notecards, proofs, photographs, microfilms, and printed materials. The Papers include the manuscript research materials and correspondence for each of his books except his biography of Theodore Dreiser. Among the correspondents are William Benton, Bruce Catton, Carey McWilliams, Mrs. Fremont Older (Cora Miranda Baggerly Older), and Thornton Wilder.