The Arnold Petersen papers, which date from 1892 to 1965, are organized in three major sections: Correspondence, Socialist Labor Party Records, and Writings. Correspondence (box 1), 1938-1964, has been arranged chronologically. The small number of items present is mostly made up of outgoing letters whose content is of a political nature.

Socialist Labor Party Records (boxes 1-11), 1892-1965, stem from Petersen's role as national secretary of the party. These materials have been divided into four subsections: Miscellaneous, Communications, National Convention Records, and Publications. The Miscellaneous group contains medals, membership cards, newspaper clippings, photographs, programs, and the presidential election vote tallies for the party since 1892. Communications include intra-party messages, open letters to public figures, reports on party activities and public statements of party policy. Many of these were written by Arnold Petersen in his capacity as secretary. The Socialist Labor Party National Convention records are organized chronologically, and include material from their conventions, which have been held in presidential election years since 1896. A published volume of the record of each convention, entitled either “Proceedings” or “Minutes, Reports, Resolutions, Platform, Etc.” is present. For the conventions in 1940 and 1964 a holograph report prepared by Petersen is also included. The subsection of party publications is organized first by type of publication. Included here are groups of books and pamphlets which treat leftist topics and themes, arranged by author and then by title. The date of publication is noted on the folders and shelf list. Although they were published by the party press, the New York Labor News Company, works by Arnold Petersen are not included here, but instead form the third major section of Writings. Also found among the publications are the leaflets printed by the party over a considerable period of time. These are divided into general and election leaflets, and most are undated. Finally there are six issues of the official party newspaper, Weekly People.

The Writings section (boxes 12-26), 1922-1964, contains the writings of Arnold Petersen. Included here are numerous articles; books; introductions and forewords to works by others; pamphlets; letters written for publication in the Weekly People; speeches; translations, mostly from the Danish, of works by others; and verse. The materials are organized alphabetically, first by type and then by title. When holograph or typescript drafts, galley proofs or published versions of the work are present, this is noted on the folders and shelf list. Frequently material originally written as an article or delivered as a speech by Petersen was reprinted as a pamphlet or a part of a pamphlet. In these cases, the work was filed under the form in which it was originally prepared, and any pamphlet version present was also placed in the pamphlet section.