Correspondence, journals and diaries, family papers, autobiographical material, travel notes, manuscripts of and other material relating to Kingsbury's books, Health in Handcuffs (1939) and Red Medicine (1933), speeches and articles, news releases, legal and financial papers, newspaper clippings, and memorabilia.

Kingsbury's professional papers (1907-1939) including correspondence, financial papers, reports, and other business records are primarily associated with his attendance at Columbia University Teachers College, his service as assistant secretary of the State Charities Aid Association in New York from 1907 to 1911, director of the New York Association for Improving the Condition of the Poor (1911-1914), and Commissioner of Public Charities of New York City during the administration of John Purroy Mitchel (1914-1918).

Includes material on other organizations with which Kingsbury was affiliated such as the American Council on Soviet Relations, America-Yugoslav Society of New York, American Association of the Red Cross, Milbank Memorial Fund, Progressive Party, Serbian Child Welfare Association of America, U.S. Work Projects Administration, and Young Men's Christian Association of the City of New York. Topics include agriculture, American-Soviet and American-Yugoslav relations, astronomy, Chinese life and culture, Eastern European relief efforts, group health insurance, multiple sclerosis, mushrooms, New Deal legislation, public health in America and the Soviet Union, socialist societies, socialized medicine, travel, tuberculosis, unemployment, venereal disease, war relief, welfare, and world peace.

Correspondents include Jane Addams, Alexander Graham Bell, Louis Dembitz Brandeis, Charles C. Burlingham, Bailey B. Burritt, Mary E. Dreier, Paul De Kruif, Albert Einstein, Homer Folks, Harry Lloyd Hopkins, Elbert Hubbard, Charles Evans Hughes, Harold L. Ickes, Walter Lippmann, Jack London, Henry Morgenthau, Sir Arthur Newsholme, Frances Perkins, Gifford Pinchot, Jacob A. Riis, Raymond Robins, Franklin D. Roosevelt, Theodore Roosevelt, and William Henry Welch.