This series contains correspondence between John Malcolm "Mac" Forbes and Ethel Cummings Forbes with the bulk of the letters dating from 1926 and 1927, written from Mac to Ethel. Courtship letters primarily discuss acquaintances, social events, future plans, and the couple's time together. In one of his first letters, written in February 1924, Mac discusses his trip with his half-brother Gerrit through French Equatorial Africa, describing the countryside, fishing dams, the French government, and African people, including a small map of the area. Some letters from 1925 to 1927 describe Mac's life at Union Theological Seminary in New York, including his friends, activities, and religious ideals. A small amount of letters written after their wedding in June 1927 primarily discuss children, home maintenance, and upcoming trips.

Ethel wrote several letters to Mac from a peace conference in Washington, D.C. in January 1928. She describes her lunch with Edith Wilson, wife of President Woodrow Wilson; attending talks by United States cabinet members; and her impressions of suffragist Carrie Chapman Catt.

Early family correspondence is that of Charles Kimball Cummings, the father of Ethel Cummings Forbes Amory, to Lydia "Lily" Paine Cummings from 1900 to 1945. Charles primarily writes to his wife from Boston and New York discussing daily life and social activities. A July 1901 letter from Sandwich, Massachusetts, describes his military drills with the Massachusetts Light Artillery, Battery A. Charles's World War I letters, written from November 1917 to January 1918, describe his experiences as an upper-class naval officer and chronicle his time aboard the U.S.S. Mount Vernon.

The series also includes many letters from Rose Dabney Forbes to her son John Malcolm Forbes, written from 1926 to 1933. Of particular interest are letters related to her involvement with the American antiwar movement, including December 1926 letters describing the Second Conference on the Cause and Cure of War in Washington, D.C. that discuss her views on the "Mexican tangle" and President Coolidge's lifting of the arms embargo; October 1930 letters from the conference of the National Council for the Prevention of War in Washington, D.C.; January 1931 letters from the annual meeting of the League of Nations in Chicago; and many other antiwar meetings and conferences.

Another large amount of correspondence is that of Lydia Cummings to her daughter Ethel Cummings Forbes Amory, written from 1929 to 1957. Lydia's letters discuss her daily life and family activities in Beverly, Massachusetts, and describe her frequent trips to Europe, including her 1931 trip to Venice and Florence, Italy, and her 1935 voyage to Hungary, Yugoslavia, and Italy.

Additional family correspondents include Ethel's brother Charles Kimball "Charlie" Cummings, Charlie's wife Elizabeth Cummings, Mac's sisters Ellen Forbes and Amelia Forbes Emerson, Amelia's husband Raymond Emerson, Mac's brother Gerrit Forbes, Mac's nephew A. F. "Al" Howland, Mac's cousin William Cameron Forbes, Ethel's sisters Evelyn Cummings and Margaret "Meg" Cummings Hinckley, and Meg's husband William Hinckley. Topics include daily life; family news; social activities; engagement and wedding congratulations; planning, construction, and maintenance of Mac and Ethel's home on Naushon Island; and family finances and trusts. Of interest are Margaret Cummings's letters from school in Paris in 1931 and at Black Mountain College in North Carolina in 1934, discussing her studies and daily life. Also of interest are the 1930 letters of W. Cameron Forbes from Tokyo, where he served as U.S. ambassador to Japan.

Later correspondence, from 1944 to 1961, is primarily that of Ethel Cummings Forbes Amory with her second husband Copley Amory and her children Holly, Joan, Beryl, Jock, and Charles. Copley's 1944 letters describe his business trips to New York and Washington, D.C.; finances; and other family matters. Letters from Ethel and the children to Copley in the summer of 1948 chronicle their trip through the western United States, describing stops in South Dakota, Montana, Yellowstone, Utah, Colorado, and New Mexico. Two 1961 letters from Ethel to Copley describe her trip to Tanganyika in present-day Tanzania.

This series contains incoming correspondence written to Ethel Cummings Forbes Amory. It includes letters from friends at a religious camp that Ethel attended in the summers of 1924 through 1926, including Henny Halsey, who sends monthly letters and prayers; courtship letters from Dave Morris in 1924 and 1925; letters from friends at Radcliffe College in 1926; letters of congratulations for her 1926 engagement and 1927 wedding to John Malcolm Forbes; and congratulations on the birth of her children. Beginning in 1930, many letters thank Ethel for her invitations and hospitality at her home on Naushon Island. Correspondents include writer Percy MacKaye, Dorothy Pomeroy of Milton, Kathleen Sproule of Cambridge, and Frances Sturgis of Boston. Letters from friends at Rollins College include those of economics professor Royal W. France and his wife Ethel France, whose letters date from 1930 to 1946. Letters from several British friends describe wartime conditions in 1940 London.

Although only a few letters mention Mac's death in 1941, several of his friends continue to correspond with Ethel, including Winthrop H. Churchill, Montfort Haslam, and Gifford Dyer Warner. Later correspondence also includes letters of thanks for Ethel's charitable works or acts of kindness, particularly her financial support of needy families in Germany. 1948 and 1949 correspondence is largely related to Ethel's work with the Society of Friends, including that of Edna Haviland of the American Friends Service Committee. 1955 letters are primarily related to the marriage of Ethel's daughter Beryl. Also included are two folders of undated correspondence.

Papers include Ethel's 1918 War Savings certificate, a 1921 list of members elected to the Junior League, 1927 Radcliffe Class Day and commencement invitations, Ethel's 1927 wedding invitation, her 1930 remarks at a prohibition meeting, memoranda of receipts and disbursements from her trust fund (1927-1933), income statements in accounts with J. M. Forbes and Co. and Shawmut Bank (1933-1934), a 1933 list of Ethel's charitable contributions, and her 1933 will. Also included are newspaper clippings related to Ethel's activities or those of her friends and family, poems by Royal France and Lillian Arnold, and undated notes.

Ethel's diary records her trips to England in 1957 and Mexico in 1959. Entries from 30 April to 3 July 1957 describe her visit to her brother Charlie, including daily details of activities and sites, people visited, books read, hotels, meals, Friends meetings, and her return trip on the Queen Mary. Included are descriptions of London, Windsor, Exeter College, Kent, the Cotswolds, Berkeley Castle, Ludlow, Wales, Warwick, Stratford, the Chelsea Flower Show, Cambridge, Salisbury, Tiverton, St. Michael's Mount, Tintagel, and Oxford.

Entries from 23 January to 20 February 1959 document Ethel's visit to Mexico City, activities, sightseeing, reading, landscapes, Friends meetings, presents bought, and letters sent. Included are descriptions of Guadalajara, San Miguel Allende, Fortin, Cordova, Oaxaca, and Taxco.

Also in this series are two small undated booklets listing items sent to the laundry with prices for washing. Entries are written in several hands.

Other than a few letter drafts written by Mac, this series contains incoming correspondence with the bulk dated between 1925 and 1933. Personal correspondence includes that of his Harvard classmates Winthrop H. "Win" Churchill, John B. "Buzzer" Paine, Montfort "Muffin" Haslam, and Gifford Dyer "Giff" Warner, who corresponded with him throughout his life. Letters from friends at Union Theological Seminary include those of George Stewart, with whom he traveled to Oregon. 1925 and 1926 correspondence largely consists of engagement and wedding congratulations. Other letters are related to the management and caretaking of Mac and Ethel's house at Naushon Island, including those from his brother-in-law Raymond Emerson and caretakers James "Bill" Robinson and A. G. Fisher.

Later letters include those of Robert Bradford, American dramatist Percy MacKaye, and Harriet Pipkorn. During Mac's studies in London in 1933 and 1934, letters from Rollins College friends, including Royal and Ethel France, Ginny Fisher, and Mary Lucas, discuss activities and controversies at the school. Other letters request financial support and acknowledge his charitable contributions to the New York School of Social Work and National Council for the Prevention of War, as well as his financial support for several Rollins College students and Russian emigrants in Paris.

A small amount of professional correspondence includes several 1926 offers of employment, as well as 1929 letters from Rollins College president Hamilton Holt and dean Winslow Anderson. Other letters are related to Mac's career in psychiatry and mental health, including correspondence with and about students and psychiatric diagnoses. 1931 letters from Dr. Thaddeus Hoyt Ames discuss his psychiatric treatment of patients.

Papers include Mac's February 1923 logistical notes in preparation for his trip to French Equatorial Africa with his brother Gerrit; an itinerary for his 1926 road trip to Portland, Oregon; notes and memoranda related to the construction of Mac and Ethel's house on Naushon Island and management of its grounds; a 1934 letter from the University of London giving Mac permission to study at Harvard University's psychology clinic, and 1935 notes on the behavior of his daughter Holly, most likely in relation to his studies of child psychology. Also included are bank statements, receipts, lease agreements, and miscellaneous undated notes.

Mac's West End Pond Lodge diary includes entries written from 1919 to 1924 describing his various visits to the lodge on Naushon Island, hunting for deer and duck, and adventures with friends.

His June 1926 western road trip diary contains reflective observations of his drive from Milton, Massachusetts, to Portland, Oregon, for his summer of missionary work while at Union Theological Seminary. The diary entries describe little of Mac's stops along the way, but record miles driven, gas purchased, driving times, and weather.

Two 1930 notebooks contain Mac's notes related to psychology classes he taught at Rollins College.