The collection consists largely of correspondence to and from important figures in American and European radical and labor movements, among them Angela Balabanoff, Clarence Darrow, Karl Marx, Eugene V. Debs, Fredrick Engels, J. Keir Hardie, Darlington Hoopes, Samuel Gompers and Leon Trotsky. Some letters from the files of the Tamiment Library to and from researchers are also part of the collection.

Also included in the collection are a significant number of typescripts and manuscripts (some in the form of photocopies) by political and literary figures such as David Ben-Gurion, Earl Browder, Elizabeth Gurley Flynn, Charlotte Perkins Gilman, Jack London and Mark Twain.

Ephemeral items include a receipt for a payment to V. I. Lenin in Switzerland, two documents from the French Revolution, a manifesto signed by Emiliano Zapata and early nineteenth century British broadsides. Handwritten Russian-language newsletters circulated by Palmer Raid deportees known as the "Ellis Island Bulletins" are also included in the collection.