This series contains the business records of the staff which produced the Encyclopaedia. It includes correspondence with Macmillan (the publisher of the Encyclopaedia), with sponsoring organizations, and with subscribers. Also present are financial records, including bills and invoices, checkbook ledgers, account books, and information on Encyclopaedia staff and salaries. Files of press notices, reviews of the Encyclopaedia, and a scrapbook of press clippings are also present in this series.

This series contains an assemblage of files used in planning the Encyclopaedia. First is a set of lists of suggested topics, arranged by broad subject field. These lists were circulated to eminent authorities in each field for comment. Each file consists of the lists, comments by the outside authorities, and related correspondence. Second there is a set, also filed by broad subject area, of outlines and abstracts of articles, including enumerations of suggested word lengths for each article. This is followed by a series of Memoranda to Authors, filed alphabetically by subject, giving the scope for each suggested article or series of related articles. A set of miscellaneous files relating to these lists and outlines follows. The remainder of the series consists of the card files used in the preparation of the Encyclopaedia. First, a set of Topic Cards with brief summaries of articles, suggested word lengths, and often notes on who suggested the topic, and possible authors for the articles. Then there is a set of Abstract Cards (A through L only), which mainly seem to include suggested authors for the articles, although some outlines and suggested word lengths are also present. Finally is a set of Biography Cards, which are identical to Topic Cards except that they treat personal name subjects.

This series contains the original manuscripts and edited drafts of the articles of the Encyclopaedia. Often included are notes on background information and statistics, as well as slips for sources consulted at the New York Public Library in the course of the factual checking done by the Encyclopaedia staff. Occasionally correspondence relating to the article will be found in these files, but most correspondence is filed in the next series.

The folders are arranged alphabetically by the title of the article.

This series contains the correspondence of the editors with the contributing authors, advisers and potential contributors. Most of the correspondence is in English, but French and German are commonly employed by European correspondents. The list of correspondents below is not exhaustive, but includes only major sets and famous names: the series as a whole contains correspondence with more than 1200 persons. Much of the correspondence with famous people, such as W.E.B. DuBois and Oliver Wendell Holmes, consists merely of polite refusals, but many, such as Margaret Mead and Felix Frankfurter, did make substantial contributions to the Encyclopaedia.

A large gap exists in this series: there are no files from correspondents with names beginning with the letter C; in fact, none between the letters BR and DR. This material was not present when the collection was first inventoried in 1984, and must have been lost prior to that time.

This series contains files of manuscripts and index cards for projected articles that were "killed", that is, not used in the printed version of the Encyclopaedia. The contents of these files correspond to those of the "live" files from which they were drawn.

This series contains the published editions of the Encyclopaedia. First is an incomplete set of the first printing, and next a complete set of the 16th printing. Finally is a complete set of the new International Encyclopedia of the Social Sciences, the successor edition published in 1968.