Correspondence, writings, subject files, clippings, and printed matter relating chiefly to Gleason's editorial work with Cosmopolitan, The Survey, and Collier's Weekly magazines; his experiences as a journalist and medic in World War I; and his activities on behalf of the British labor movement, Bureau of Industrial Research, United Mine Workers of America, and socialism. Subjects include immigration, Jews in the U.S., American isolationism, the Irish question, and religious groups and sects in southern California.

Individuals represented include Jane Addams; John Blankenhorn; Bruce Bliven; John Brophy; Robert W. Bruère; James Bryce, Viscount Bryce; G.K. Chesterton; Herbert David Croly; Andrew Furuseth; Percy Stickney Grant; Frank Hodges; Vida Dutton Scudder; Robert Smillie; Charles Proteus Steinmetz; Norman Thomas; Ili︠a︡ L'vovich Tolstoĭ; and Charles Richard Van Hise.

Correspondents, in addition to Gleason's wife, Helen Hayes Gleason, and other family members include Roger N. Baldwin; Edward William Bok; Geoffrey G. Butler; Edward C. Carter; Winston Churchill; Fannia M. Cohn; Joe Cook; Eugene V. Debs; George Eastman; Walter Prichard Eaton; Richard Henry Edwards; Joseph Fels; Felix Frankfurter; Lewis Gannett; Armand Hammer; Norman Hapgood; Alfred Harcourt; Sidney Hillman; J.J. Jusserand; Paul Underwood Kellogg; Thomas Kirkup; Edward B. Krehbiel; Harry Wellington Laidler; Harold Joseph Laski; Ludwig Lewisohn; Walter Lippmann; Jack London; A. Lawrence Lowell; Julian W. Mack; Paul Elmer More; William Morrow; James Oppenheim; C.H. Parkhurst; Eustace Percy, Baron Percy of Newcastle; William Lyon Phelps; John S. Phillips; Charles Mulford Robinson; Edward Alsworth Ross; May Sinclair; William Andrew Spalding; Mark Sullivan; William Simon U'Ren; Lillian D. Wald; Andrew Dickson White; William Winter; and Stephen S. Wise.