Research and Writings, consists of a potpourri of personal essays, book reviews, research inquiries, and speeches that span nearly a fifty year period. Of perhaps the most interest is De Leon's 1974 credo of atheism; his 1925 one act musical drama presented at The League for Industrial Democracy conference; his book review of Robert Hoxie's Trade Unionism in the United States (undated); and his 1926 speech to The League for Industrial Democracy entitled "Communism in the USA."

Unions, consists of both printed and nonprinted materials including resolutions, organizational histories, pamphlets, newspaper clippings, flyers, meeting notices, and arbitration briefs from theBakery and Confectionery Workers, The National Marine Union, and The United Office and Professional Workers. Also included is correspondence from. 1943 1944 between De Leon and various union officials concerning exhibits and arbitration briefs, and bitter correspondence from 1964 1965 between De Leon and the president's office of The National Marine Union concerning the abolition of De Leon's position of assistant research director of that organization.

Workers' Education, consists of course syllabi from Margaret Daniels, Solon De Leon, David Saposs, and A.L. Wilbert for courses taught to workers in conjunction with The International Ladies' Garment Workers' Union and The Jefferson School of Social Science. Also included is an outline by Martin Beardslee of John Cannon's History of Labor in the United States and a lecture by De Leon for The United Labor Education Committee.

Political Organizations, consists of printed materials from The League for Industrial Democracy and The Southern Conference Education Fund. The League for Industrial Democracy materials consist of form letters, ballots, flyers, reports, and pamphlets from 1955 1958, while The Southern Conference Educational Fund materials consist of speech transcripts, form letters, minority caucus resolutions, policy committee report positions, and a newspaper (the Southern Patriot) from the years 1973 1975 that chronicle internal political disputes over party ideology and strategy. Also included is correspondence from 1956 1965 between De Leon and League for Industrial Democracy members including Sidney Henchberg, Harry Laidler, Andre Shifften, and Norman Thomas that focus upon De Leon's disenchantment with the League's lack of organizational activism as well as a 1974 letter to Ann Braden and Penny Lane of The Southern Conference Education Fund.

Applications, consists of college transcripts from Columbia and The City College of New York, inquiries, correspondence, and application forms, both Empty and filled out, for teaching, labor research work, and federal civil servant positions. Also included are letters of recommendation and personal resumes.

Personal, consists of a collection of poetry of aesthetic and political orientation, either typewritten or clipped from newspapers and magazines, including a few works of poetry by De Leon himself; and an informal scrapbook that contains clippings on humorous subjects.

Addendum, consists almost exclusively of letters sent and received by De Leon concerning specific ideological and party procedure disputes with the Socialist Labor Party in the form of typewritten and handwritten correspondence as well as letters clipped from the letters to the editor column of The Daily People and Weekly People. Correspondents include such party notables as Daniel De Leon and Arnold Petersen. Also included is a political allegory of the class struggle written by Solon De Leon and entitled "Step At A Time And Something Now."

This series contains additional correspondence and papers related to Solon De Leon's involvement in labor organizing and education. Correspondence ranges from personal letters from friends spanning several decades to more formal correspondence with organizations with which De Leon was affiliated, including the Rand School of Social Science, League for Industrial Democracy, and the Socialist Labor Party. These records also contains a number of teaching materials related to classes De Leon taught to union workers. These materials also contain some of De Leon's personal writing including plays, sketches, and short stories. It also contains a number of biographical materials related to his father Daniel De Leon.