This series consists primarily of correspondence spanning several generations of families related to Henry Fairfield Osborn.

Materials are organized into the following five subseries:

Subseries I.1, Correspondence of Sturges, Cady, Perry and Osborn family members, includes correspondence of HFO's maternal grandparents, Jonathan Sturges and Mary (Cady) Sturges; his parents, William Osborn and Virginia (Sturges) Osborn; and various other members of the Cady family. Henry Fairfield Osborn's personal correspondence with his wife, Lucretia ("Lulu") Perry Osborn, is also included, along with other Perry family correspondence, primarily between Lulu and her mother, Josephine Perry.

Early correspondence between Jonathan and Mary Sturges describes transportation and travel, food, health and medical care in the 1830's.

Cady family correspondence includes letters between Mary (Cady) Sturges and her mother Elizabeth Cady, her aunt Olive Cady, and her sister Elizabeth Cady (later Mrs. Hamilton Murray). Letters span the period from 1832 to 1888, and discuss family news, health and events of daily life.

Correspondence of the children of Jonathan and Mary Sturges includes letters by and between Virginia Osborn's siblings and their families, including a letter from J.P. Morgan, who married Virginia's sister Amelia Sturges. Amelia died of tuberculosis shortly after their marriage, and Morgan's letter to Jonathan Sturges, written December 28, 1861, describes her critical condition.

Of particular interest is a folder of letters between Mary Sturges and her Fredericksburg friend Jane Beale, who remained in Virginia during the Civil War. The letters were written after the war, and describe the difficulties the confederate Beale family endured during and after the conflict.

Subseries I.2, Correspondence of Osborn family children, contains correspondence of HFO's four surviving children (Virginia, Perry, Fairfield Jr., and Josephine) from early childhood, when they were away at boarding school, to adulthood, and includes many letters from their travels abroad.

Subseries I.3, Other family papers and photographs, includes genealogical and biographical information about the various families; a small number of business, and legal papers, including wills and deeds and leases for family property; several folders of ephemera and photographs, including a few of HFO on an expedition in Egypt; and passports and visas issued to Henry and Lulu Osborn in the 1920's and 1930's. This subseries also includes a poignant memorial album for HFO's sister Virginia Reed Osborn, who died when she was only 20 years old.

Subseries I.4, Correspondence and clippings of Lucretia Perry Osborn, includes materials relating to Lulu Osborn's activities outside the family circle, including several boxes of correspondence and clippings, primarily concerning her 1927 monograph Washington in His Own Words.

Subseries I.5, Journals, consists of bound journals, including an 1868 datebook of William Osborn (from Europe), several diaries and "common place books" of Virginia Osborn (1850-1851, 1871, 1875), and an 1883 journal of Lulu Perry.

Series II, Henry Fairfield Osborn papers, is organized into five subseries. (Note that this Series does not include the family correspondence of Henry Fairfield Osborn, which is found in Series I, Family Papers.)

Subseries II.1, Correspondence and related materials, includes HFO's non-family correspondence, primarily with professional colleagues and scientist friends. The most frequent correspondent is HFO's Princeton classmate and fellow paleontologist William Berryman Scott. Their letters (foldered separately) discuss both personal news and professional matters.

The remaining correspondence is foldered chronologically, and includes frequent letters between HFO and British evolutionary biologist Sir Edward B. Poulton. Other notable correspondents include Howard Crosby Butler, Charles F. Dawes, Seth Low, John Muir, John Stewart Kingsley, and Edith Roosevelt. Topics include professional research, publications and speaking engagements, and news about colleagues and friends.

Subseries II.2, Associations and honors, includes correspondence and other papers relating to HFO's numerous memberships in professional and social organizations and clubs, and his many honorary degrees, medals and decorations. Notable memberships include several organizations that promoted eugenics and/or racial purity, including the American Eugenics Society, the American Genetic Association, the Aryan Society, and the Galton Society. HFO was also a member of the exclusive Zodiac Club, along with J.P. Morgan, and this subseries includes invitations to dinners and other Zodiac Club correspondence. There are also several folders of correspondence relating to alumni events at Princeton. In addition, there is material relating to tributes in honor of HFO's birthdays, his retirement from AMNH and various other occasions.

Subseries II.3, Speaking engagements and publications, includes programs and announcements of some of HFO's lectures, and drafts of a talk ("What a Girl Can Do") and article on the topic of suitable occupations for women. Also included are articles by HFO on religion and evolution and on the history of the New York Zoological Society, which HFO founded (now known as the Wildlife Conservation Society, it manages the Bronx Zoo, Central Park Zoo, Prospect Park Zoo, Queens Zoo and the New York Aquarium). There are also several folders of notes and drafts, and several folders of correspondence with Charles Scribner's Sons, who published multiple books by HFO.

Subseries II.4, Professional appointments and biographical information, contains material relating to HFO's tenure as President of the American Museum of Natural History (1908-1933). This includes correspondence and papers relating to the "Bumpus Affair" of 1910-1911, a conflict over exhibits between HFO and AMNH director Dr. H.C. Bumpus which resulted in the latter's resignation, and correspondence concerning the Roosevelt Memorial (cornerstone laid in 1931). Also included is one folder of material relating to HFO's appointment as a professor at Columbia University, and some biographical articles and notes.

Subseries II.5, Journals, consists primarily of annual leather-bound datebooks kept by HFO between 1899 and 1935. These contain both professional and personal notations, regarding appointments, engagements, travel and scientific observations, birthdays of friends and families, and significant events. Clippings, calling cards and similar materials were sometimes inserted next to related entries; to retain context, these have not been removed so researchers should be careful when handling.

There are also a few more extensive travel and expedition journals: 1867-68, 1871 (Europe), 1879 (Coburg/London), 1885 (Germany), 1913 (Western United States), and 1922 (China/Mongolia).

This series consists mainly of transcriptions of primary material found elsewhere in the collection, including some of Osborn's correspondence and a few journal excerpts. Also included is a typewritten extract relating to Osborn and the Princeton Scientific Expedition to the West in 1877 from "W.B. Scott: Materials for an Autobiography." There are also several pieces of oversize ephemera, including a 1931 certificate of appreciation issued to Henry Osborn as one of the Founders of the Save the Redwoods League.